| Lock and Dam No. 26 | |
| Image Alt: | Old Lock and Dam 26 and the Old Clark Bridge with a swing span rail bridge in between. |
| Country: | USA |
| Location: | Alton, Illinois |
| Status: | D |
| Construction Began: | 1939 |
| Demolished: | 1990 |
| Dam Crosses: | Upper Mississippi River |
| Dam Length: | 600 ft |
Lock and Dam No. 26 was a lock and dam located near Alton, Illinois on the Upper Mississippi River around river mile 202.5.
Opened in 1938, its largest lock was 600 feet long. It was demolished in 1990 and replaced by the Melvin Price Locks and Dam, which is also known as Lock and Dam number 26.