Port Union is an unincorporated community in western West Chester Township, Butler County, Ohio, United States, on State Route 747 about three miles north of Springdale and three miles southeast of Hamilton. The town was laid out in 1827 by William Elliott alongside the turning basin for the Miami and Erie Canal and was about midway between Crescentville and Hamilton on the canal. It was originally known as McMaken's Bridge, but took the name its township.. The Cincinnati, Hamilton, and Dayton Railroad later laid tracks through Port Union.