Route 128 is a short highway in Grundy County.

Its northern terminus is at Crowder State Park northwest of Trenton; its southern terminus is less than three miles (5 km) south at Route 146.

Despite being an even number, which normally runs east-west in Missouri, Route 128 is a north-south highway.

Route 128 begins at an intersection with Route 146 west of Trenton, heading north as a two-lane undivided road.

Route 128 curves west and reaches its northern terminus within the state park.