Grand Lake St. Marys State Park sits along the shores of Grand Lake St. Marys in Auglaize County, Ohio — a lake that holds the distinction of being the largest inland lake in the state. Originally constructed as a reservoir to feed the Miami and Erie Canal in the 1840s, this massive body of water spans over 13,000 acres and gives the surrounding 14,091-acre state park its character.

The lake is the main draw here. Boating, sailing, and fishing dominate warm-weather months, with anglers targeting crappie, catfish, and perch across the shallow, sprawling waters. A public launch ramp and marina make getting on the water straightforward. Back on land, the park offers picnic areas with shelters, swimming beaches, and trails that wind through the flat western Ohio landscape — a mix of open meadows and scattered woodlands that feels distinctly different from the state’s hillier parks to the south and east.

Birding is quietly excellent along the lake’s marshy edges, particularly during spring and fall migration when waterfowl gather in impressive numbers. The flat terrain also makes this a welcoming park for families with young children or anyone looking for easy, accessible outdoor time.

Summer is peak season, with the lake at its liveliest from June through August. Spring and early fall offer quieter visits and better fishing conditions. Winter brings a stillness to the area, though ice fishing draws a dedicated local crowd when conditions allow.

Grand Lake St. Marys rewards visitors who come for the water and stay for the wide-open calm of rural western Ohio.

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