| Willoughby Run | |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Pennsylvania |
| Subdivision Type3: | Region |
| Subdivision Name3: | Adams County |
| Subdivision Type5: | Township |
| Subdivision Name5: | Cumberland |
Willoughby Run is a tributary of Marsh Creek in Adams County, Pennsylvania in the United States.
Willoughby Run flows southward between Herr Ridge and McPherson Ridge through the Gettysburg Battlefield.