Census.gov - the definitive source for census data.
American Fact Finder - provides access to data about the United States, Puerto Rico and the Island Areas. The data in American FactFinder come from several censuses and surveys. American Fact Finder will be retired in July of 2019.
data.census.gov - Starting in July, data.census.gov will be the primary way to access Census Bureau data, including upcoming releases from the 2018 American Community Survey, 2017 Economic Census, 2020 Census and more. After July 1, 2019, all new data (previously released on American FactFinder) will be released on this new data platform.
Census Academy - Your virtual hub for learning data skills.
ProQuest Statistical Abstract of the U.S. - authoritative and comprehensive summary of statistics on the social, political and economic conditions of the United States
HardtoCount2020 - Mapping Hard to Count (HTC) communities for a fair and accurate 2020 census.