In 1814, Isaac Bigelow travelled to the area from Centre County, Pennsylvania to pay for land purchased from his uncle, then returned to Pennsylvania to study medicine with his father. He returned in 1817, and settled in the Pleasant Valley area in 1818. He hired a surveyor named David Chapman, and laid out the town of Westminster on June 11, 1818. At the time, Westminster lay wholly within Darby Township in Madison County. In 1820, when Union County was formed, the county line was moved to the middle of Westminster. In 1823, the previous survey was resurveyed, additional territory was incorporated, and the town's name was changed from Westminster to Pleasant Valley. From 1832 to 1851, there were six additions to the town limits. In 1851, due to there already being another town in Ohio named Pleasant Valley, the town changed its name to Plain City.