Search through the digital version of the 1940s United States Census
I kind of stumbled upon this by accident. I had no idea that The New York Public Library made the 1940s U.S. Census available to the public for free, from the comfort of your home. The US National Archives is responsible for digitizing all 3.9 million items from the Census and you can view and search the entire archives for you or your family members.
The 1940s Census is an important one because it captures the state of the country during the Great Depression.