Start at the home page of major organizations. Investigate A-Z lists, search boxes, top tabs, side menus.
Open pdfs of comprehensive reports, look at their list of references.
Start at these two resources:
Follow-up by looking at the broader data in these resources:
To cite U.S. Census data using APA, treat the information under the guidelines of Government Documents. Do not simply cite “US Census website” but the specific sources, i.e. “Demographic Profile”
U.S. Census Bureau (year data was published). Name of data or report. Retrieved from [URL].