Lakes / Ohio / Grand Lake St. Marys
Grand Lake St. Marys, Ohio
13,356 acres
Surface Area
14 ft
Max Depth
140.26 mi
Shoreline
869 ft
Surface Elevation
Where It Sits, and How Deep It Goes
Locator - Ohio
40.53 degrees N, 84.50 degrees W - Mercer County. State and county outlines drawn from Census boundary data; the lake marker is placed by its Ohio DNR coordinates, not by eye. Schematic - not a survey map.
Depth Profile - Grand Lake St. Marys
Schematic cross-section drawn to one shared depth scale - not a survey or bathymetric map.
How Grand Lake St. Marys Stacks Up
- The largest lake counted in Ohio by surface area - 13,356 acres.
- A shallow lake - typical of most Ohio lakes, which run under 20 ft at their deepest.
- About 88 miles from Columbus, as the crow flies.
Facts and Figures
Waterbody IDoh-grand-lake-st-marys-39107
CountyMercer
Shoreline140.26 mi
Coordinates40.5260, -84.5009
Deepest Natural Lakes in Ohio
| # | Lake | County | Surface Area | Max Depth |
|---|---|---|---|---|
| 1 | McKarns Lake | Williams | 40 acres | 75 ft |
| 2 | Portage Lakes | Summit | 474 acres | 60 ft |
| 3 | Punderson Lake | Geauga | 80 acres | 55 ft |
| 4 | Wolf Run Lake | Noble | 208 acres | 51 ft |
| 5 | Barton Lake | Williams | 19 acres | 42 ft |
Largest Lakes in Ohio
| # | Lake | County | Surface Area | Max Depth |
|---|---|---|---|---|
| 1 | Grand Lake St. Marys | Mercer | 13,356 acres | 14 ft |
| 2 | Mosquito Creek Lake | Trumbull | 7,212 acres | 24 ft |
| 3 | Indian Lake | Logan | 5,161 acres | 12 ft |
| 4 | Seneca Lake | Noble | 3,550 acres | 21 ft |
| 5 | Berlin Lake | Portage | 3,344 acres | 60 ft |
Sources: Ohio Department of Natural Resources lake data (ID oh-grand-lake-st-marys-39107); USGS. Verified October 28, 2026.