Plain City is a village in Madison and Union counties in the U.S. state of Ohio, along Big Darby Creek.

[5] After 1795, as white settlers began moving into the region, the area around present-day Plain City was referred to as Pleasant Valley.

This name remained in use into the 20th century, appearing in the Ohio Guide of the late Depression era.

He hired a surveyor named David Chapman, and laid out the town of Westminster on June 11, 1818.

[7][8] At the time, Westminster lay wholly within Darby Township in Madison County.

In 1823, the previous survey was resurveyed, additional territory was incorporated, and the town's name was changed from Westminster to Pleasant Valley.

[8] Previous to 1850, Plain City was a smaller trading point than Amity, but after a trunk-line for the Atlantic and Great Western Railroad was laid through its corporation limits, business and manufacturing increased dramatically.

[11] The village has grown in recent years with the addition of new housing developments.

Darby Fields on the south side of the village broke ground in 2017.

[citation needed] Darby Station on the east side of the village broke ground in 2022.

[18] Each year, during the month of July, the village hosts the Miami Valley Steam Threshers show at Pastime Park, which showcases antique tractors, steam threshers and other farm equipment.