American Libraries, a journal of the American Library Association, listed the 1939 Alexandria Library sit-in first in its timeline of sit-ins at segregated public libraries.  The sit-in, organized by Samuel Wilbert Tucker, was carried out by five courageous young American American men. The next sit-in didn’t happen until  1960.  https://americanlibrariesmagazine.org/2017/06/01/i-always-will-refuse-civil-rights-library-sit-in/

   Alexandria (VA) Library, August 21, 1939