Powell, Ohio. Powell is an affluent city in Delaware County, Ohio, United States. The population was 11,500 at the 2010 census. The community was first settled around 1801, two years before Ohio became a state. It was named Middlebury at the time, because the first settlers came from the Middlebury, Connecticut area. In 1857, Judge Thomas Powell established the first post office in the community, and the residents decided to adopt his name.