Hancock County is a county in the U.S. state of Iowa. As of the 2020 census, the population was 10,795. The county seat is Garner. The county was founded on January 15, 1851, and named in honor of John Hancock, a leader of the Continental Congress during the American Revolution.

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.