Aylmer is a town in Elgin County in southern Ontario, Canada, just north of Lake Erie, on Catfish Creek. It is 20 kilometres south of Highway 401…Aylmer is a town in Elgin County in southern Ontario, Canada, just north of Lake Erie, on Catfish Creek. It is 20 kilometres south of Highway 401, and is almost equidistant between the United States cities of Detroit and Buffalo.