Charles City is a city in and the county seat of Floyd County, Iowa. Charles City is a significant commercial and transportation center for the area. U.S. Routes 18 and 218, Iowa Highway 14, and the Canadian National and Canadian Pacific railroads serve the city. The population was 7,396 at the time of the 2020 census, a decrease of 5.3%, from 7,812 in 2000.

U.S. Highway 18 (US 18) is the northernmost east–west United States Numbered Highway in the state of Iowa. As with all state highways in Iowa, it is maintained by the Iowa Department of Transportation. It enters the state by crossing the Big Sioux River between Inwood and Canton, South Dakota. It travels about 312 miles (502 km) and connects Spencer, Mason City, and Charles City. The highway leaves the state via the Marquette–Joliet Bridge over the Mississippi River at Marquette. Prior to becoming a U.S. Highway, the route US 18 follows was known as Primary Road No. 19 and the National Parks Pike.