The Trustee Records series contain the official records as maintained by the Board of the Church. This primarily consists of the resolutions of the Board and meeting minutes for regular meetings, annual meetings, and committee meetings.

Annual Meetings and Trustee Meetings cover finances, attendance, buildings, music, the Sunday school and other major concerns of the Congregation. In addition to minutes, annual meetings files include correspondence, reports, and other documents introduced to the Board over the course of the meeting. Reports presented to the Trustees by the Treasurer, the Pastor, and various committees are also collected in a dedicated ledger of reports. Some committees of note among these reports are the Female Samaritan Society, the Willow Place Chapel committee, the Music and Organ committees, and the various clubs that were a part of the Church's activities. Reports by the Pastor include information on deaths and baptisms in the Church. The Auditor's reports presented to the Trustees are grouped together in a separate folder.

Some of the correspondence and resolutions of the Trustees, particularly those pertaining to the early days of the church and its formation, can be found in the "History" folders within the Subject Files series.

Some bound material, including the Reports Ledgers and the Society Meeting Minutes, include indexes of the contents of the ledgers, pointing out subjects and events. The indexes to the Society Meeting Minutes include lists of officers and the members of various committees. The early By-Laws (as of 1843) of the Society can also be found within these bound meeting minutes.

The series also contains some minutes of meetings of a Joint Committee of the 1st and 2nd Congregations from around the time of their split and attempted reconciliation in the 1840s.

The Subject Files series collects the files kept by the Church covering its various interests and activities.

Of particular note are the "History" files which contain documents related to the early formation of the Congregation. These files include correspondence between the founders, resolutions and other actions of Trustees, early lists of subscribers, By-Laws, and early bills and accounts. The documents address the incorporation of the Congregation, the acquisition of land and the building of the Church of the Saviour, ministers, music, and other major matters of the congregation. Documents related to the early formation of the 2nd Congregation can also be found among these "History" folders. Some other documents related to the early and foundational years of the church can be found in the folders on By-Laws, Covenants and Statements of Faith, and Special Services. Also of interest are documents on the Church's work with children and youth including various clubs and very early documents regarding the Church's Sunday School. There is also club work here regarding psychiatric social work and counseling made available to parishioners during the tenure of John H. Lathrop. Researchers interested in the Low family should also note one file regarding the family with documents mostly unrelated to the church dating back to 1790.

Subject Files also holds published directories of the Church which have Parish lists, club reports with member rolls, updated by-laws and other information on the Church. Some of these directories have been annotated, particularly in the Parish membership lists. Other family-oriented documents include the Bequests, Memorials, Special Services, and membership files.

The Ministers series contains files kept regarding the installation, resignation, and other major matters for the ministers of the Church of the Saviour. The materials are primarily correspondence and copies of resolutions and votes of the Society on these matters. Some files also include sermons, relevant news clippings, and articles . The file on Frederick W. Holland has correspondence regarding protest and controversy over his leadership during a developing schism in the Church as well as his record of funerals, baptisms, and marriages in the Church during his tenure. Clippings and Orders of Service related to Alfred E. Goodnough, H. Price Collier, and Samuel A. Eliot can be found in the Scrapbooks series. Additional sermons by H. Price Collier can also be found in the Scrapbooks series.

In the case of John Lathrop there are several folders due to the bulk of material. These are broken up by subject including his installation, committees he was involved with, other churches he communicated with, and memorial services after his death. Some of the committees here include the the League of Nations Association, the Long Island Historical Society, the Religious Arts Guild, refugee aid associations and other organizations dealing with ecumenical issues, the peace movement, and welfare and aid to the needy. While these files relate to what the Church kept in regards to Lathrop, for documents related to Lathrop's work, including his sermons, see the John H. Lathrop Files series.

The John H. Lathrop Files series contains the working and reference files of John H. Lathrop who served as minister to the First Unitarian Congregation of Brooklyn from 1911 to 1967. The series covers Lathrop's varied interests and prolific work. Lathrop's work within the Church and community can be seen through his sermons, correspondence, parishioners' files, and work with organizations like the Brooklyn Urban League which he helped found and managed as president for many years. As minister for the Church during both world wars, Lathrop was interested in the international peace movement. Lathrop was involved with various organizations which mobilized for peace like the War Resisters League, the Emergency Peace Campaign, and the National Peace Conference, which he headed. Lathrop was similarly interested in international aid and outreach and had files pertaining to humanitarian efforts in Germany, Spain, Hungary and other nations.

There are some records within this series regarding the First Church's connection to Unitarians in Transylvania and their church there. Several files also address Czechoslovakia and the Unitarian Service Committee trip there which Lathrop was a part of. The First Unitarian Congregation of Brooklyn had a special connection to Czechoslovakia as a former member of the Church, Charlotte Garrigue, had married the first president of Czechoslovakia, Tomas Garrigue Masaryk. Lathrop kept up correspondence with their daughter, Alice Garrigue Masaryk, one of the founders of the Czechoslovak Red Cross, and their son, Jan Masaryk, the Foreign Minister of Czechoslovakia.

The series also contains a collection of reference material on various topics of interest to Lathrop including marriage, peace, labor and unemployment, religious freedom, liberal Christianity, and other related issues. These reference files consist of articles, pamphlets, and various materials from organizations Lathrop was interested in or with which he was tangentially involved. Lathrop's sermons deal with this broad range of topics as well, particularly ideas of liberal Christianity and its application in the world. Lathrop's work with like-minded organizations like the International Association for Liberal Christianity and Religious Freedom and the American Committee on Religious Rights and Minorities can be found in this series.

Some files on Lathrop and documents created by him can be found in many other series within the collection, but particularly within the Ministers series which contains documents on his installation, organizations he served on the board of, and memorial services for his death.

The Unitarian Movement Files contain the general files kept by the Church on its involvement with the Unitarian movement across America, primarily through the American Unitarian Association (AUA), and in other parts of the world. The AUA material concerns Unitarian outreach, publicity, and social-service. There is one folder related to the congregation's sister church in Transylvania. For more on the Church's efforts abroad, see the John H. Lathrop Files for papers on Czechoslovakia, Hungary, Transylvania, and the Philippines.

The Sunday School Books series contains small books and ledgers used by the Sunday School of the First Unitarian Church. Lists of names of teachers and students can be found in the Attendance Records Ledgers and the Directory and Secretary's Book. The books on the Annual Meetings of Teachers and the Sunday School Journal account the operations and concerns of the school. Sunday School classes were conducted by the Church of the Saviour at the Wall Street Ferry House on Furman Street until the building of Willow Place Chapel in 1876. Thus, it should be noted that the books in this series span the time before and after the building of the chapel and those interested in the Congregation's Sunday School should also check the Willow Place Chapel series. Some additional records on the Church's school can be found in the Subject Files series. Some financial records of the Sunday School can be found in the Financial Records series.

The Calendars series contains the bound books that hold the orders of worship as well as flyers and pamphlets related to services. Programs to special services and events are often included as well. Some of the calendars were in the possession of Minister John H. Lathrop and include some of his annotations and notes. For additional orders see the files on "Sermons and Orders of Worship" within the John H. Lathrop Files

The registers in this series track the christenings, marriages, and funerals carried out by the Congregation. Willow Place Chapel had its own functions separate from the Church of the Saviour and kept its own registers which can also be found in this series. The Willow Place Chapel registers also contain substantive commentary on the families making up that portion of the Congregation, including notes on employment, illness, marital problems, and other issues. Some registers also contain additional information on the Sunday School and charity loans. For additional records of christenings, marriages, deaths, and member rolls of the Church, one should check the reports of the Ministers to the Trustees in Trustee Records, the "History" folders within the Subject Files, and lists of parishioners kept by John H. Lathrop in the John H. Lathrop Files.

The Buildings and Construction series pertains to buildings constructed, purchased, and maintained by the First Congregation. Among these buildings is the Gothic Revival style Church of the Saviour of the Brooklyn Heights neighborhood, built in 1844. The series includes the original plans and specifications submitted by its architect, Minard Lafever. In addition to plans, specifications, and alterations made on the buildings, the series contains financial information related to the properties and documents on embellishments to the buildings such as the Church's stained glass windows and marble baptismal font. There is also information on the pews of the Church of the Saviour and some of its renters. In addition to the Church of the Saviour other buildings in this series include the Parish House (50 Monroe Place), the Parsonage (98 Pierrepont St), the Pierrepont Chapel (adjacent to the Church of the Saviour), and 123 Pierrepont Street. Documents related to Willow Place Chapel and Columbia House are collected in the Willow Place Chapel and Columbia House series. For information on the organ of the Church of the Saviour refer to the Subject Files series.

Willow Place Chapel was built in 1876 under the direction of Alfred T. White who was seeking a more proper setting for the settlement school under his charge. The Chapel functioned somewhat separately from the Church of the Saviour and conducted its own evening services as well as adopting the First Congregation's Sunday School. In addition to these tasks, some other classes (such as in music or sewing), clubs, and welfare work operated out of Willow Place Chapel. In 1906 Columbia House was added to the settlement complex and carried on its own outreach and community work in conjunction with Willow Place Chapel. The Willow Place Chapel and Columbia House series contains the records related to the work carried on within these buildings and on behalf of the members including annual and trustee reports, deacon meeting minutes, Sunday school records, and the records of the Chapel Association. The series also holds relevant building records in regards to construction and alterations, financial information including accounts and salaries, various records on clubs and events that functioned out of the Chapel, and records related to health and social work carried out by the Chapel's staff. Prior to the establishment of Willow Place Chapel these tasks, particularly social and settlement work, were done at the Furman Street Mission. Reports and other records relevant to work done at the Furman Street Mission can be found in this series, particularly among material before 1876.

For more on the Congregation's Sunday school, see the series Sunday School Books. For registers pertaining to services and members of the Willow Place Chapel, see the Registers series. Some financial records of the Sunday School can be found in the Financial Records series.

The Financial Records series holds many of the Church's records regarding collecting and disbursing funds for its operations as well as for Willow Place Chapel, the Sunday School, Missionary Fund, and other programs. General financial statements of the Congregation are within this series. The series includes records of disbursements from the Charity Fund, Friendship Fund, and Minister's Discretionary Fund (the Charity Fund was used to make payments to congregants in need until 1923 when it was replaced by the Friendship Fund. The Friendship Fund was closed in 1940 and its purpose subsumed into the Minister's Discretionary Fund, which was also used for such payments prior to 1940.) In addition to the records of the Treasurer, budgets, investments, and fund raising, this series also contains ledgers on subscriber dues and pew rentals, including a book of the original deeds to the pews. Records on the receipts of the Church and ledgers of Offerings to the Church are another source of lists of pews renters and subscribers. The Church's investments include mortgages, so there is some information on individual residential mortgages including amounts, debtors, and properties.

The Housekeeping Scribe's Chronicle is a record of expenses for club meetings and events and thus doubles as a resource of menus and club member rolls.

The books in the Scrapbooks series contain clippings and ephemeral items related to the Church. The scrapbooks collect articles on the church's ministers and on religious and ecumenical matters. They also collect some published images, poems, hymns, and local news items. Several of the scrapbooks include clippings related to Plymouth Church and Henry Ward Beecher. Most of the scrapbooks seem to have been made by members of the church. The scrapbooks of items on the ministers Alfred E. Goodnough, H. Price Collier, and Samuel A. Eliot and the scrapbooks collecting the sermons of Collier were assembled and donated to the church by Maud Willard Bartlett. One other scrapbook ("Religion and Theology, 1866-1875") included a note that it came from the home of Mary E. Butterick in 1942.

The Photographs series contains photographs from two separate photo accessions related to the Church. Most of the folders in this series contain images that were originally part of the First Unitarian Congregational Society records. These photos were initially removed from the collection and entered into the library's image database under a V1989.20 accession number. The photos include church buildings, like Willow Place Chapel and the Third Unitarian Congregation's Unity Church, and church activities such as a picnic, fairs, plays, and some minstrel shows. Also included are photos of ministers from the First, Second, and Third Unitarian Congregations including John Lathrop, John White Chadwick, Alfred P. Putnam and Stephen H. Camp. The last folder in the series contains photos from a later accession, V1990.46, and consists of four print reproductions of photographs of Willow Place Chapel, Columbia House, and the school at the chapel.

Item level description and digital versions of images from the collection are available for searching via the image database in the library.

The Second Unitarian Congregation first split from the First Congregation in 1840 over dissatisfaction with Minister Fredrick Holland. The congregations united in 1842 (after Holland's resignation) but split again in 1851. The Second Unitarian Congregation series represents the records of the Second Unitarian Congregation during both of these splits.

The Congregation's first permanent minister was Samuel Longfellow, installed in 1853. The Second Unitarian Congregation took a progressive stance under Longfellow who occasionally preached against slavery and delivered an infamous sermon in praise of John Brown. Some of Longfellow's sermons can be found in the file on him. A parishioner's complaint and resignation of his pew in reaction to Longfellow's John Brown sermon can be found in the "Finances: Pew Rentals" folder. Longfellow's tenure was followed by Nahor A. Staples who also included abolitionist views in his sermons. The Second Congregation's influential minister John White Chadwick (installed 1864) is also well represented in this series through his correspondence, sermons and articles written by and about him, particularly memorials after his death.

The series contains records related to the regular functions and activities of the Second Congregation including trustee records, financial records of pew renters and subscribers, committee reports and record books kept by the Sunday School. The series also contains many records of the Second Congregation's Branch Alliance, a women's group that did charity work and eventually folded into the First Congregation's Samaritan Alliance when the Congregations reunited in 1924.

The Third Unitarian Congregation was established in 1867 in order to accommodate parishioners of the First Unitarian Congregation who had been travelling from the Fort Greene and Clinton Hill neighborhoods to attend services at the Church of the Saviour in the Brooklyn Heights neighborhood. Frederick A. Farley assisted in duties as a minister until the Third Congregation installed Stephen H. Camp as minister in 1869. Camp became the Third Congregation's most prominent minister and in addition to encouraging organized charitable works and teaching within the Congregation's Sunday School he also shepherded the Congregation from their first space in Unity Chapel (built in 1868 with the assistance of the First Congregation) to Unity Church (built in 1886). The Third Congregation sold its church and united with the First Congregation in 1925.

The Third Unitarian Congregation series contains the records of the Third Congregation's organization and operation including its by-laws, society and trustee minutes, resolutions, and financial records. The series also contains records of the Congregation's charitable work such as through the Branch Alliance, the Charitable Fund, the Ladies Benevolent and Social Society, and other clubs and groups organized by the Church. Correspondence regarding the merger of the Third Congregation's merger with the First Congregation can also be found here.