Grand Lake St Marys State Park
State Park · Ohio · Ohio Department of Natural Resources
- Camping
- 14,091 acres
Grand Lake St Marys State Park surrounds Grand Lake St Marys, a 13,500-acre reservoir in western Ohio near St Marys. The Ohio Department of Natural Resources manages the park, which totals 14,091 acres of land and water; the park's land base covers 591 acres, with the remaining acreage made up of the lake itself. The agency describes the lake as originally built as a feeder reservoir for the Miami-Erie Canal, and for many years it was recognized as the largest man-made reservoir in the world.
It suits boaters, anglers, and campers drawn to a large, shallow inland lake rather than visitors seeking rugged backcountry hiking. Camping, day-use areas, historic features, recreation facilities, and trails make up the park's amenities, spread across 198 mapped points of interest. Its scale and calm, shallow water shape most of what happens here, from wide-open boating to shoreline fishing and swimming beaches strung around the lake's edge.
Plan your visit
Camping & lodging
13 mapped camping locations
Site types & reservations: see the official site.
Know before you go
- Address
- 834 Edgewater Drive, St Marys, OH, 45885
- Phone
- (419) 394-3611
- Official site
- ohiodnr.gov
- Managed by
- Ohio Department of Natural Resources
- Hours
- 6am to 11pm. Visitors are permitted to actively engage in legitimate recreational activities outside these hours. If you have questions, call the park office.
Getting there
834 Edgewater Drive, St Marys, OH, 45885
Directions on Google Maps →On the ground
The Dam/Spillway stands as one of the park's two named historic features, a reminder of the lake's origin as a canal-feeder reservoir. Trails here are short and mostly paved: the West Bank Multi-use Trail runs 1.2 miles and the East Bank Multi-use Trail runs 1.4 miles, both accessible, while the Red Wing Hiking Trail covers 0.65 mile within the campground. Hikers can also follow a connection from the park down to the historic Miami and Erie Canal feeder junction, linking to the Miami-Erie Trail and Buckeye Trail for those wanting a longer walk beyond the park boundary.
The lake itself is the park's real feature. Its 52 miles of shoreline are ringed by a 300-foot no-wake zone, while unlimited horsepower boating is allowed on the open water, and eight state-operated launch ramps give boaters access. Anglers fish for largemouth bass, white and black crappies, bluegills, walleye, channel and flathead catfish, yellow perch, bullheads, and carp, with accessible fishing available at a pier on East Bank and an access area on West Bank. Four public swimming beaches operate during daylight hours. Before the lake was built, the area was a wet prairie and forest landscape stretching from the Allegheny mountains of Pennsylvania to the prairies of Illinois, and the park today contains woodlands, wetlands, and prairies alongside surrounding croplands. Grand Lake St Marys was also the site of the first offshore oil drilling in the world, with more than 100 oil wells installed and operated over the lake's waters between 1891 and about 1913.
Photos
Practical notes
Park hours run from 6am to 11pm, though visitors engaged in legitimate recreational activities may remain beyond that window. The park office can be reached at (419) 394-3611, and the address is 834 Edgewater Drive, St Marys, OH, 45885.
Nearby parks
Parks of Ohio
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Browse all Ohio parks →Sources: State agency, Wikimedia Commons / editorial, USGS PAD-US, Google Places · updated 2026-08-23