The western terminus of SR 604 is at a T-intersection with US 42 in Jackson Township approximately 5 miles (8.0 km) southwest of West Salem.

Its eastern terminus is at the intersection that doubles as the southern split of the concurrency of SR 94 and SR 585 in Chippewa Township nearly 1.5 miles (2.4 km) southeast of Rittman.

State Route 604 passes through one incorporated community along its path, Congress, where it meets SR 539.

State Route 604 travels through the counties of Ashland and Wayne.

No portion of this state highway is included within the National Highway System, a network of routes deemed most important to the country's economy, mobility and defense.