Originally constructed as a feeder reservoir for the Miami-Erie Canal, Grand Lake St. Marys was for many years recognized as the largest man-made reservoir in the world. This large lake is the gateway to swimming, boating, camping and fishing in one of Ohio's oldest state parks

Although hard to imagine, at one time the Grand Lake St. Marys region was part of a vast forest wilderness that stretched from the Allegheny Mountains of Pennsylvania to the prairies of Illinois. Today, in place of this forest are fields of corn, soybeans and wheat.

In addition to forests, pre-settlement Ohio contained large prairies and wetlands. The land which now lies beneath St. Marys reservoir was once a vast wet prairie. Today, the park contains varying habitats including woodlands, wetlands, and prairies in addition to the surrounding croplands.

Grand Lake St. Marys lies along one of the country?s major migration routes. Water birds using the lake as a resting stop include Canada geese, ducks, grebes, swans, egrets, loons, herons, cormorants and ospreys. Many ducks, geese and heron also nest here. Bald eagles, magnificent birds long absent from the area, have again nested on the southwest corner of the lake at the wildlife refuge. Other animals of the park include fox squirrel, mink, raccoon, beaver, coyote, white-tailed deer and many others.

The area in and around Grand lake St. Marys State Park played an important part in the development of the Northwest territory. The St. Marys River served as a vital link between the Great Lakes and the Ohio River. Because of this heavy water traffic, the renegades Simon and James Girty established a trading post, which eventually evolved into the town of St. Marys. General ?Mad? Anthony Wayne passed through the area during the War of 1812, and some of his men returned here to make their homes.

In 1837, work commenced on a reservoir for the Miami-Erie canal to maintain the canal?s five-foot water depth. Workers using hand tools were paid 35 cents a day and a jigger of whiskey to keep malaria away. At its completion in 1845, 13,500-acre Grand Lake was the largest man-made lake in the world. The lake was connected to the canal by a three-mile feeder. The canal prospered until the coming of the railroads in the 1870s. The area experienced another boom in the late 1890s when oil was discovered. For a time the lake was dotted with oil derricks. Today a pile of rocks near the center of the lake marks the spot of the last producing well.

Grand Lake St. Marys and other canal feeder lakes in the state were the first areas to be dedicated as Ohio state parks in 1949.

Ohio does not have an annual pass and does not charge entrance fees to state parks.

The campground contains 216 sites of which 154 are equipped with electricity. Facilities include flush toilets, laundry, showers and a dump station. Pets are permitted. The campground also offers a camper's only swimming beach, boat launch and boat docks/tie-ups. Five spacious Cedar Cabins with all the amenities of a fully-equipped RV are also available for daily or weekly rental. A seasonal naturalist holds scheduled programs, including movies, Thursday through Saturday night.