Iowa 3 begins at the Big Sioux River where it continues west into South Dakota as South Dakota Highway 50. Shortly after entering Iowa, the highway intersects Iowa 12. Iowa 3 traffic turns north onto Iowa 12 and the two highways travel together toward Akron. There, the two highways split as Iowa 3 heads east toward Le Mars where it meets U.S. Highway 75 (US 75) and its its business route. The highway continues east toward Remsen and Marcus where it meets Iowa 140 and Iowa 143 in each respective town. At Cherokee, the highway intersects US 59 and skirts the northeastern edge of town. North of Aurelia, Iowa 3 meets Iowa 7. Northeast of Truesdale, Iowa 3 intersects US 71.