State Route 604 (SR 604) is an east–west state highway in north central Ohio. 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.

Created in the late 1930s, this primarily rural route traverses the northeastern corner of Ashland County and the northern tier of Wayne County. 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.

SR 604 was first designated in 1937 along the path through northeastern Ashland County and northern Wayne County that it occupies to this day. The highway has not experienced any major changes since making its debut.

County	Location	mi	km	Destinations	Notes
Ashland	Jackson Township	0.00	0.00	US 42 – Ashland, Medina
Wayne	Congress Township	4.40	7.08	SR 301 south (Elyria Road) – Lattasburg	Western end of SR 301 concurrency
		4.52	7.27	SR 301 north (Elyria Road) – West Salem	Eastern end of SR 301 concurrency
	Congress	7.20	11.59	SR 539 north (West Salem Road)	Western end of SR 539 concurrency
		7.56	12.17	SR 539 south (Maple Street)	Eastern end of SR 539 concurrency
	Canaan Township	10.98	17.67	SR 83 (Burbank Road)
		15.77	25.38	SR 3 (Cleveland Road) – Wooster, Creston, Medina
	Milton–Chippewa township line	23.05	37.10	SR 57 (Wadsworth Road) – Rittman, Orrville
	Chippewa Township	24.13	38.83	SR 94 (Mt. Eaton Road) / SR 585 (Akron Road) – Wooster, Norton
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus