St. Marys
- County:
- Elk County
- County Seat:
- No
- Area (mi²):
- 99.316
- State:
- Pennsylvania
St. Marys is a city located in Elk County, Pennsylvania. St. Marys has a 2026 population of 12,361. St. Marys is currently declining at a rate of -0.39% annually and its population has decreased by -2.82% since the most recent census, which recorded a population of 12,720 in 2020.