Photo: 1940 Census publicity photo. Harry L. Hopkins Collection. FDR Presidential Library and Museum.
We continue to appreciate the historic release of 1940 Census records (particularly the Census worker pictured above who must be kind of hot).
The visualization below compares county level change in total population between 1930 and 1940. The graphic highlights the effect of the dust bowl, with large declines in rural, agricultural regions. California and Florida grew, as did Detroit and other cities in what today we call the rust belt.