St. Mary's on the Flats, originally known as the Church of Our Lady of the Lake, was the first Catholic church building in Cleveland, Ohio. The location where the church once stood can be found, in an 1881 atlas, at the south-east corner of Columbus Ave. and then Girard Ave. on the east bank of the Cuyahoga river in the flats. Irishtown Bend Archeological District, where many of the parishioners lived, lies to the west, across the Cuyahoga river in what was Ohio City. Ohio City was annexed by Cleveland on June 5, 1854.