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.

Iowa Highway 182 (Iowa 182) is a 9-mile-long (14 km) state highway in the northwestern corner of Iowa. It begins at U.S. Highway 18 (US 18) in Inwood and ends at Iowa 9 southeast of Larchwood. The highway has been in the primary highway system since 1930, when it was known as Iowa 26. On January 1, 1969, Iowa 26 and Iowa 182 swapped designations.