Old St. Mary's Church is a parish church of the Roman Catholic Archdiocese of Cincinnati in the United States. It is located at 123 E. Thirteenth Street in the Over-the-Rhine neighborhood of Cincinnati, Ohio. This Roman Catholic parish was organized in 1840 by German immigrants, at a time of dramatic growth in the city's population. Designed in the Greek Revival style by Franz Ignatz Erd, it is the second-oldest German-Catholic parish in the city and the oldest standing church in Cincinnati.