Grand Lake St. Marys State Park is a public recreation area located on 13,500-acre (5,500 ha) Grand Lake in Mercer and Auglaize counties, Ohio. Grand Lake is the largest inland lake in Ohio in terms of area, but is shallow, with an average depth of only 5–7 feet (1.5–2.1 m). The state 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. It is west of St. Marys, and south-east of Celina, 23 miles (37 km) south-west of Lima in the north-western part of Ohio.