In recent years the Census Bureau has made their data products accessible via online tools thus simplifying the search process for users. However, it is not a simple process if you need historical census data so various reference tools will help. Census data collection and processing procedures are complex; census data products are voluminous, varying in format and content; glossaries associated with census programs and tabulations are unique. As a result, the Census Bureau publishes general and specific reference publications to aid researchers in understanding and utilizing its census data products. In addition, other reference publications using census data are published by individuals or commercial vendors offering academic, business, and practical approaches. Although there are many types of reference publications, they tend to generally fall into the following categories: catalogs, guides, and indexes.
Following is a very selected list of reference publications that exist for individual censuses or a range of censuses. The types of reference publications available for each census will vary, and there may not be a specific reference publication for some censuses. Where possible, an attempt has been made to include reference sources that cover census history, user's guides or subject indexes that provide additional information on subject content and coverage, special indexes (e.g., to tables in census reports, state area report numbers, census tract reports, titles of census report series and current population and industrial reports), and to provide links to the Library of Congress catalog records to aid in retrieving census reports from the Library's collections
In recent years more and more government publications, including those by the Census Bureau, have been digitized and made available to the public through Hathi Trust Digital Library External and Internet Archive External. Besides, Census Bureau has revamped digitization of their publications and a lot of them are now available on the U.S. Census Bureau website. We have included links to the digital versions when available, but we recommend that you check these digital libraries in case what you need has been added.
Catalogs provide information on specific data products for each decennial census by type and subject area. The following materials link to fuller bibliographic information in the Library of Congress Online Catalog. Links to additional online content are provided when available.
Catalog of United States Census Publications, 1790-1945. by United States Catalog of Census Publications 1946-1972 by Bureau of the Census Catalog of Publications, 1790-1972. by Circular of Information Concerning Census Publications, 1790-1916 by 
Dubester's U. S. Census Bibliography with Sudocs Class Numbers and Indexes by Census Catalog and Guide by Basic guides and user's guides primarily focus on providing specific detail on operations and activities involved in planning and carrying out the censuses as well as guidance and technical documentation in using specific data products. Indexes generally provide assistance in accessing specific types of census data products, such as a subject index to current population reports. The following materials link to fuller bibliographic information in the Library of Congress Online Catalog. Links to digital content are provided when available.
Census Tract Manual, 5th ed. by Population Information in Nineteenth Century Census Volumes by Population Information in Twentieth Century Census Volumes, 1900-1940 by Population Information in Twentieth Century Census Volumes, 1950-1980 by Topical Index of Population Census Reports, 1900-1930 by 
Understanding the Census by United States Decennial Census Publications, 1790-1970Bibliography and Reel Index; a Guide to the Microfilm Edition of United States Decennial Census Publications, 1950-1960. by 
