128 volumes of the Official Records provide the most comprehensive, authoritative, and voluminous reference on Civil War operations.
Sources in U.S. History Online is a series of archival digital collections intended for public library patrons as well as high school, community college, and university students. The Civil War digital collection contains nearly 500 significant documents of the time--personal narratives, monographs, regimental histories, collected essays, sermons, songs, legal tracts, and political speeches--enabling students, faculty and patrons to study one of the key events in American history.
For St Johns County residents, in addition to access at the library, this database can be accessed from home with your library card. This is probably true of other locations whose libraries have the database.