The vast majority of the letters date from the 1930s. Some of the correspondents are the Reverend Spence Burton, William Thurston Brown, Edward Filene and publisher Alfred Harcourt. McNamara also received letters from John Dewey, Fremont Older, Lincoln Steffens. Clarence Darrow, and Communist Vita Marcantonio. Writers Upton Sinclair and Irving Stone also corresponded with McNamara. Rebecah Rainey, Mattie Smentoski, and Margaret Wilson were women who regularly wrote J.B. and kept him informed about current events, particularly labor news.