Overpeck is an unincorporated community in central St. Clair Township, Butler County, Ohio, United States. It has a post office with the ZIP c…Overpeck is an unincorporated community in central St. Clair Township, Butler County, Ohio, United States. It has a post office with the ZIP code 45055. It lies between New Miami and Trenton. Overpeck is a part of the Cincinnati-Middletown-Wilmington, OH-KY-IN Combined Statistical Area.