NOAA’s Office of Coast Survey’s Historical Map and Chart Collection “contains over 20,000 maps and charts from the late 1700s to present day. The Collection includes some of the nation’s earliest nautical charts, hydrographic surveys, topographic surveys, geodetic surveys, city plans and Civil War battle maps.” It’s a huge, searchable database; the large files (several megabytes each) are in MrSid format, for which you will need the appropriate plugin. Thanks again to peacay.