Plainville is a census-designated place (CDP) in Columbia Township, Hamilton County, Ohio, United States.

Plainville is located in a valley on the banks of the Little Miami River, opposite Newtown and adjacent to Mariemont and Indian Hill.

Plainville is part of the Greater Cincinnati area and the Mariemont City School District.

[7] According to the United States Census Bureau, the CDP has a total area of 0.077 square miles (0.2 km2), all land.

[10] According to the U.S. Census American Community Survey, about 0.0% of the population were living below the poverty line.