American FactFinder - This tool is one of the most essential in gathering information. This searchable tool helps navigate demographic data from several different surveys. The statistical information is presented in table form and organized into subject areas, including health, business, and population. The Advanced Search can also help yield statistics on topics such as marital status, SNAP recipients, limited English speaking households. This tool can yield information at the state, parish, and city level. Note that city level data will depend on whether the area is in the Census or not
NOTE: As of July 2019, all new Census Bureau data will be released via data.census.gov
Data.census.gov - This tool will be replacing the American FactFinder starting July 2019. It covers the same demographic data, but allows users to view and customize data tables prior to downloading them. Since it is still being developed, this tool is likely to change frequently. Please ask me if you need assistance locating information.
State and County QuickFacts - This tool presents fewer, more condensed demographic statistics in a variety of subject areas. While not a substitute for the American FactFinder, it can be easier to locate some information here (such as population density.) This tool can yield information at the state, parish, and city level. Note that city level data will depend on whether the population is at least 5000.
StatsAmerica - This online resource from Indiana Business Research Center (Indiana University) gathers statistics from numerous sources and combines them into an interface focused on usability. They acknowledge the sources of their data, and much of it comes from government sources. While not a substitute for other sources, it may be easier to locate some information here or a source to investigate in more depth from here.