The 1940 United States Senate election in Pennsylvania was held on November 5, 1940. Incumbent Democratic U.S. Senator Joseph F. Guffey successfully sought re-election to another term, defeating the Republican nominee, Jay Cooke.
As of 2023, this is the last time that Mifflin County and Montour County voted Democratic in a Senate election. This was also the last time until 1991 that Democrats won this Senate seat, and the last until 2006 that they were elected to this seat for a full term.
|- |-bgcolor="#EEEEEE" | colspan="3" align="right" | Totals | align="right" | 3,997,020 | align="right" | 100.00% | align="right" |