Its northern terminus is approximately 1 mile (1.6 km) east of Helena at a T-intersection with US 6.

SR 635 travels through northwestern Seneca County and southwestern Sandusky County along its way.

The highway is not included as a part of the National Highway System, a network of highways deemed to be most important for the nation's economy, mobility and defense.

Its original routing between SR 18 in Bascom and US 6 near Helena is the same one that it utilizes to this day.

No significant changes have taken place to the alignment of SR 635 since it was established.