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Database of American Libraries before 1876
This tightly focused resource is a database of "institutional and commercial libraries that existed in what is now the continental United States from the time of first settlement through 1875," including searchable records on almost 10,000 libraries.

This database originated from boxes of punched cards that sat in the office of their compiler, Haynes McMullen, a professor emeritus of library science at the University of North Carolina, Chapel Hill. McMullen started collecting the data when he discovered a document -- Public Libraries in the United States of America: Their History, Condition, and Management. Special Report. Part 1 -- published by the U.S. GPO in 1876. Although this 1,222 page report offered information on libraries existing in the year 1876, there was no data on libraries before that time.