This series consists of personal correspondence between Prendiville and numerous individuals. Of note are two folders of letters between Prendiville and Gerald O'Reily, a prominent member of the New York City Transit Workers Union (TWU) and a contemporary of TWU President Mike Quill. Materials in the correspondence concern Irish Republicans Frank Ryan and Father Michael O' Flanagan.

This series consists of original letters, newspaper clippings, periodicals, and form letters collected by Prendiville on Irish republican politics and the escape and rescue of Fenian prisoners held in Western Australia by the American whaling ship the Catalpa in the late 19th century. The series includes publications produced by The Workers Party (Ireland), including a manifesto, newsletters, pamphlets, and issues of the Student Workers Party Bulletin. Periodical titles include The Irish Felon, The Felon, The Harp, Voice of Freedom, and Irish Republican Newsletter. The form letters were sent by the National Association for Irish Justice and the National Association for Irish Freedom.

This series consists of administrative papers, government forms, and other documents related to Freedom of Information Act (FOIA) requests and appeals made by Prendiville from 1986 to 1994. The files contains photocopies of memoranda, letters, and reports generated by the Federal Bureau of Investigation (FBI) in the course of their surveillance of Irish Republican activities in the United States between 1930 and 1979. Also included are newspaper and magazine articles, brochures, and other literature distributed by Irish American organizations under investigation. Many files contain collections of clippings from Irish publications, especially newspapers produced by support groups, that no longer exist and for which there may be no surviving copies. Organizations present in this series include the Irish Republican Clubs, Clan na Gael, James Connolly Clubs, the Irish American Labor League, the Irish Republican Army (IRA), Irish Republican Clubs (IRC), National Association for Irish Freedom (NAIF), the National Association for Irish Justice (NAIJ), and The Citizens for Irish Justice (CIJ). Specific individuals such as James Gralton and James Larkin also appear. Much of the material is heavily redacted.

This series consists of flyers, pamphlets, broadsides, and other materials demonstrating support for various 20th century Irish Republican and Irish American support groups.

This series consists of flags, sashes, bumper stickers, and other objects demonstrating support for various 19th and 20th century Irish Republican and Irish American support groups. Also included is Prendiville's button collection, an assortment of political buttons from Irish organizations in Ireland and the United States, including Irish Republican Clubs, Irish Northern Aid, Citizens for Irish Justice, and the National Association for Irish Freedom. Complementing the buttons are detailed notes on the objects, created and supplied by Prendville.