South Dakota's state highways were assigned in a numbering pattern that followed that of the U.S.

Highways followed upon their inception.

East–west highways carried even numbers and increased from North to South – while north–south highways carried odd numbers and increased from east to west.

This holds true only for two-digit highways.

Three-digit highways follow the odd–even routing, but they do not sequentially remain near a "parent" route as a spur or alternate route and instead are independent of any parent two-digit route.