The National Archives, state and local archives, libraries, and genealogical organizations have a wealth of information that supplements decennial census records. This information includes colonial and state censuses, mortality records, schedules from agriculture and economic censuses, immigration records, land records, and obituaries.
For more information, visit your local library to inquire about their holdings and the availability of local records. The National Archives' Resources for Genealogists includes links to their resources and information about records held elsewhere.