Sub-series 1.1: Annual Reports includes annual reports of the Long Island Historical Society submitted to New York State and sent to members from 1894 to 1958. There are no annual reports from the years 1870-1874 and most of the years post-1966. Annual reports post-1966 can be found in Series 2: Board and Committee records.

This sub-series also includes examples of annual reports and annual appeals from 1997 to 2000 from other New York City- and Brooklyn-based institutions, such as the Brooklyn Museum.

Sub-series 1.2: Constitution and by-laws includes 1863 certificates of incorporation of the Long Island Historical Society and by-laws and amendments to by-laws through the 1980s.

Further files about amendments to by-laws can be found in Series 2: Board and Committee records.

Sub-series 1.3: Deeds, mortgages, and leases includes deeds, mortgages, and leases related to the 128 Pierrepont Street building. The leases are rental agreements between the Long Island Historical Society and various companies for using space on the ground floor.

Related materials are in Series 5: Building records.

Sub-series 1.4: Staff management includes files regarding union organizing at the Long Island Historical Society and Brooklyn Historical Society, staff lists, senior meetings, holiday schedules, the Jim Laughlin Executive Director search, and employees from the New York City Department for the Aging.

Further materials regarding staff management at the Long Island Historical Society and Brooklyn Historical Society can be found in Series 3: Executive Director files and Series 4: President files.

Sub-series 1.5: Strategic planning includes proposals, memos, and correspondence related to organizational and change management processes. Most of the materials relates to the name change process and feedback in the mid-1980s when the Long Island Historical Society changed its name to Brooklyn Historical Society and strategic planning proposals from 2007 to 2019.

Further files related to strategic planning and fundraising can be found in Series 10: Development.

Sub-series 2.1: Board of Trustees, Board of Directors, Executive Committee, and Annual Meeting materials, 1863 - 2020, includes agendas, minutes, and memos related to the Long Island Historical Society and Brooklyn Historical Society's Board of Trustees, Board of Directors, Executive Committee, Annual Meeting, and special committees.

Sub-series 2.2: Carol Clark Board and Executive Committee files includes agendas, memos, minutes, correspondence, handwritten notes, and other material related to Carol Clark's time as President of the Brooklyn Historical Society.

Sub-series 2.3: Jessie Kelly Board and Executive Committee files includes agendas, minutes, memos, correspondence, and handwritten notes related to the Board of Trustees meetings and Executive Committee meetings around Jessie Kelly's time as President of the Board, Chairman of the Board, and President of the Brooklyn Historical Society.

Sub-series 2.4: James Laughlin Building Committee files, 1997 - 2002, includes files from the Building Committee that oversaw the building renovations in the late 1990s and early 2000s. The files include correspondence, memos to the Executive Committee and Board of Directors, and plans and agreements produced by the York Hunter construction services.

Sub-series 2.5: Board of Trustees biographical files includes correspondence, questionnaires, news clippings, and obituaries related to former trustees of the Long Island Historical Society and the Brooklyn Historical Society.

Sub-series 2.6: The Women's Committee of the Long Island Historical Society contains annual reports, financial records, meeting minutes, membership lists, brochures, and material related to the Children's History Room program. The financial records include correspondence, dues slips, receipts, bills, and financial reports. The committee kept a file for each major exhibit, benefit, and tour they organized. These files consist of postcards, correspondence, budget information, and invitations.

This sub-series also contains four scrapbooks that document the activities of the Women's Committee through photographs, newspaper clippings, brochures, and other documentation.