Grand Lake St. Marys State Park is an American state park, west of St. Marys, and south-east of Celina, 23 miles (37 km) south-west of Lima in the north-western part of Ohio. Grand Lake covers 13,500 acres (5,500 ha) in Mercer and Auglaize counties. Grand Lake is the largest inland lake in Ohio in terms of area, but is very shallow, with an average depth of only 5 to 7 feet (1.5 to 2.1 m). The park is open for year-round recreation, including boating, fishing, swimming and hunting. The park consists of the lake and park facilities scattered all around the shore intermingled with private property and a facility operated by Wright State University.