The USGS now allows downloads of ALL historic maps this is a treasure trove for map lovers. Below is from the USGS webpage

The goal of The National Map’s Historical Topographic Map Collection (HTMC), which started in 2011, is to provide a digital repository of USGS 1:250,000 scale and larger maps printed between 1884, the inception of the topographic mapping program, and 2006. The National Geospatial Program (NGP) is accurately cataloging and creating metadata to accompany highresolution, georeferenced digital files representing the legacy lithographic maps. These maps are either no longer available for distribution in print or are being replaced by the new generation of US Topo maps.

Go here: http://nationalmap.gov/historical/ to read about the program and download maps.