This lists songs that hit number one on the charts in the US during 1940. If a song spent nonconsecutive weeks at number one, the number of weeks for each occurrence at the top is shown in parenthesis.
| Date | Artist - Title | Weeks at #1 |
| November 26 1939 – January 20 1940 | Frankie Masters - Scatter-Brain | 8 |
| January 21 – February 3 1940 | Tommy Dorsey - All the Things You Are | 2 |
| February 4 – April 27 1940 | Glenn Miller - In The Mood | 12 |
| April 28 – June 15 1940 | Glenn Miller - The Woodpecker Song | 7 |
| June 16 – July 6 1940 | Glenn Miller - Imagination | 3 |
| July 7 – 13 1940 | Mitchell Ayers - Make-Believe Island | 1 |
| July 14 – 20 1940 | Glenn Miller - Fools Rush In (Where Angels Fear To Tread) | 1 |
| July 21 – October 12 1940 | Tommy Dorsey - I'll Never Smile Again | 12 |
| October 13 – December 14 1940 | Bing Crosby - Only Forever | 9 |
| December 15 1940 – March 8 1941 | Artie Shaw - Frenesi | 13 (12) |
10 different songs hit number one in the US during 1940.