The Holland Marsh is a wetland and agricultural area in Ontario, Canada, about north of Toronto. It lies entirely within the valley of the Holland River, stretching from the northern edge of the Oak Ridges Moraine near Schomberg to the river mouth at Cook's Bay, Lake Simcoe. In its entirety it comprises about 21,000 acres (8,500 hectares), with two distinct divisions. Historically it has simply been referred to as "the marsh".