Digitized maps available freely online from various archives and libraries:
Digitized urban planning documents and maps of St. Louis, from various organizations (in date order). Note: of the many planning documents in existence, these represent only ones available in full-text online
St. Louis neighborhood maps and information:
In WU Special Collections, the Harland Bartholomew and Associates Collection is a wonderful source for detailed maps of St. Louis in the 20th century. This large collection also includes many other metropolitan areas.
Image above from HBA Series 2, black Vol 53, part 1
Items in the Harland Bartholomew and Associates Collection include:
In addition to Special Collections, various types of historic maps are located in Washington University Libraries. See especially subject headings:
Looking for maps of other cities, states, or places? Try these resources: