St. Mary
- County:
- Marion County
- County Seat:
- No
- Area (mi²):
- 0.778
- State:
- Kentucky
St. Mary is a city located in Marion County, Kentucky. St. Mary has a 2026 population of 140. St. Mary is currently declining at a rate of 0% annually and its population has increased by 0.72% since the most recent census, which recorded a population of 139 in 2020.
The median household income in St. Mary is $47,500 with a poverty rate of 3.4%. The median age in St. Mary is 34.6 years: 37 years for males, and 31.2 years for females. For every 100 females there are 72.9 males.