Nested Areas (Large to Small)
In Decennial & ACS datasets:
In ACS datasets:
The major source for demographic data in the United States is the U.S. Census Bureau. This government agency produces a several surveys; the two major ones are:
Decennial Census: What is generally called "the census" (or sometimes "Census of Population & Housing"). Survey of the entire U.S. population, performed once every 10 years (2010, 2000, 1990, etc. back to 1790).
ACS (American Community Survey): A more detailed survey, performed more frequently than the Decennial Census (different areas on a rolling basis). If the decennial census data is too outdated or not detailed enough, you may use the ACS instead. See: Subjects included in the ACS
Other surveys produced by the Census Bureau include:
Once you know which survey data you need, you must then choose which source from which to get that data.
The NYC Department for the Aging has a couple of reports on the elderly population:
Counting Unauthorized Immigrants
Here's a great article on this topic from Pew Research, who has a respected estimate on the undocumented population:
Unauthorized Immigrants: How Pew Research Counts Them and What We Know About Them
The Dept. of City Planning's Chapter 7 of Newest New Yorkers 2013 discusses the undercount of the undocumented and how they make estimates.
Counting the Homeless
NYC Department of Homeless Services
Provides statistics and reports on shelter populations.
Coalition for the Homeless
Authored the 2020 State of the Homeless Report.
HOPE (Homeless Outreach Population Estimate) NYC
Each year, this volunteers from this group count unsheltered people in parks, subways, and other public spaces. This is a helpful parallel to the shelter population statistics (above).