Lakes / Maryland / Montgomery County / Triadelphia Reservoir
Triadelphia Reservoir, Maryland
794 acres
Surface Area
Where It Sits, and How Deep It Goes
Locator - Maryland
39.21 degrees N, 77.02 degrees W - Montgomery County. State and county outlines drawn from Census boundary data; the lake marker is placed by its USGS National Hydrography Dataset coordinates, not by eye. Schematic - not a survey map.
How Triadelphia Reservoir Stacks Up
- Ranks #5 for surface area among the Maryland lakes counted so far - 794 acres.
- The largest lake in Montgomery County among those counted.
- About 22 miles from Baltimore, as the crow flies.
Lakes Nearby
| Lake | County | Distance | Surface Area |
|---|---|---|---|
| Rocky Gorge Reservoir | Montgomery | 7.8 mi | 655 acres |
| Lake Bernard Frank | Montgomery | 8.9 mi | 52 acres |
| Lake Kittamaqundi | Howard | 8.9 mi | 29 acres |
| Centennial Lake | Howard | 9.0 mi | 46 acres |
| Lake Elkhorn | Howard | 9.7 mi | 33 acres |
| Lake Whetstone | Montgomery | 10 mi | 29 acres |
Straight-line distance between lake centers.
Facts and Figures
Questions About Triadelphia Reservoir
How Big Is Triadelphia Reservoir?
Triadelphia Reservoir covers 794 acres in Montgomery County, Maryland.
What Is the Largest Lake in Montgomery County?
Triadelphia Reservoir is the largest lake in Montgomery County, at 794 acres.
Largest Lakes in Maryland
| # | Lake | County | Surface Area | Max Depth |
|---|---|---|---|---|
| 1 | Deep Creek Lake | Garrett | 3,679 acres | - |
| 2 | Liberty Lake | Carroll | 2,920 acres | - |
| 3 | Loch Raven Reservoir | Baltimore | 2,200 acres | - |
| 4 | Prettyboy Reservoir | Baltimore | 1,508 acres | - |
| 5 | Triadelphia Reservoir | Montgomery | 794 acres | - |
All 78 Maryland lakes ranked by surface area
Sources: USGS NHD (The National Map NHD MapServer layer 12) named waterbodies FTYPE 390/436; counties via Census point-in-polygon lake data (ID 81714683). Verified October 30, 2026.