| Election Name: | 1940 United States Senate election in Delaware |
| Country: | Delaware |
| Type: | presidential |
| Ongoing: | no |
| Previous Election: | 1934 United States Senate election in Delaware |
| Previous Year: | 1934 |
| Next Election: | 1946 United States Senate election in Delaware |
| Next Year: | 1946 |
| Election Date: | November 5, 1940 |
| Image1: | Jamestunnell.jpg |
| Nominee1: | James M. Tunnell |
| Party1: | Democratic Party (US) |
| Popular Vote1: | 68,294 |
| Percentage1: | 50.63% |
| Party2: | Republican Party (US) |
| Popular Vote2: | 63,799 |
| Percentage2: | 47.30% |
| U.S. Senator | |
| Map Size: | 200px |
| Before Party: | Republican Party (US) |
| After Party: | Democratic Party (US) |
The 1940 United States Senate election in Delaware took place on November 5, 1940. Incumbent Republican U.S. Senator John G. Townsend Jr. ran for re-election to a third term in office, but was defeated by Democrat James M. Tunnell. This was the only seat that Democrats flipped during this cycle. This was the last time Democrats won Delaware's Class 1 Senate seat until Tom Carper's victory over Senator William Roth in 2000.