1940
Four of the ten cities here would have their first ever population drop in 1940. Though slight, they would presage a precipitous decline that started in 1950. The 1940 Census was the Sixteenth. The Census Bureau provides a list of the 100 largest cities in that year.
| Rank | City | State | Population | Notes |
| 1 | New York | New York | 7,457,995 | |
| 2 | Chicago | Illinois | 3,396,808 | |
| 3 | Philadelphia | Pennsylvania | 1,931,334 | First ever population drop for Philadelphia. |
| 4 | Detroit | Michigan | 1,623,452 | |
| 5 | Los Angeles | California | 1,504,277 | |
| 6 | Cleveland | Ohio | 878,336 | First ever population drop for Cleveland. |
| 7 | Baltimore | Maryland | 859,100 | |
| 8 | St. Louis | Missouri | 816,048 | First ever population drop for St. Louis. |
| 9 | Boston | Massachusetts | 770,816 | First ever population drop for Boston. |
| 10 | Pittsburgh | Pennsylvania | 671,659 | Last appearance in the top 10. |
Read more about this topic: Largest Cities In The United States By Population By Decade