Historical Census Browser (University of Virginia) - the data presented here describe the population and economy of U.S. states and counties from 1790 to 1960.
The National Archives - copies of the enumeration district maps available for the 1880-1940 Censuses can be purchased.
1940 Census - available free of charge at the National Archives web site.
National Historical Geographic Information System - provides, free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2010.
Before the development of the current census geography (tracts and blocks), the Census Bureau used city voting wards as census divisions. Therefore, in order to use the schedules (name lists) for the censuses between 1790 and 1900 most effectively, it is necessary to know the ward boundaries of major cities.
The Library of Congress compiled a Ward Maps of United States : A Selective Checklist of Pre-1900 Maps in the Library of Congress. (MAPS +Z 6028 .U575 W2) The Map Collection has microfiche copies of the 232 maps described in this list (OLIN MICROFICHE 1546). There are also photographic copies of each map available for New York State -- Albany, Brooklyn, Buffalo, New York City and Rochester. These are located in the catalog under the subject heading: City name--Administrative and political divisions--Maps.
For maps of cities and towns not listed in this bibliography, consult Cartographic Records of the Census Bureau (MAPS CD 3026 A32 no. 103). This lists enumeration district maps available for the 1880-1940 Censuses . If no maps are shown as being available, it means that even the National Archives cannot help. If listed, the Archives can be contacted to purchase a photocopy of the map (http://www.nara.gov).
Volume 1 of the 1940 Census of Population includes maps of Metropolitan Districts and Census Tracts for each state. Metropolitan districts were set up for the 1940 Census in each city of having 50,000 or more population in 1930, and for each Borough in New York City. Volume 2 includes maps of urbanized areas by state. The exact external boundaries of the Urban areas are described, segment by segment. Minor civil divisions are reported by wards. A series of volumes of Analytical Maps show housing characteristcs for each city, by blocks.
HUSCO 1790-1999 : historical United States county boundary files.
ArcView shapefile format county boundary files for the contiguous United States from each decade from 1790 through 1990 (also 1999). Files include county and state names as well as FIPS identification numbers and county area estimates. Territories enumerated by the U.S. Census are also included.
Olin Library Maps Disk G3701.S1 H87x 1999.