Sanborn Fire Insurance Maps
The Sanborn Fire Insurance Maps Collection at the US Library of Congress is worth mentioning separate from the other map collections held by the Library of Congress. The physical collection contains over 50,000 holdings with only about 2,600 available online.
The Sanborn Maps were originally created for assessing fire insurance liability in urbanized areas in the United States. The maps include detailed information regarding town and building information in approximately 12,000 US towns and cities from 1867 to 2007.
The map volumes contain an enormous amount of information. Information most relevant to genealogical researchers includes: an index of streets and addresses; a ‘specials’ index with the names of churches, schools, businesses etc.; and a master index indicating the entirety of the mapped area and the sheet numbers for each large-scale map. The maps include outlines of each building and outbuilding; street names; property boundaries; house and block number; and even the names of most public buildings, churches and businesses.
Check local research libraries (i.e., at major universities) to see if they have regional collections of Sanborn maps.