The southern terminus of SR 203 is at a four-way stop intersection with SR 37 just 0.50 miles (0.80 km) northwest of the city limits of Delaware.

Its northern terminus is at SR 309 approximately 4 miles (6.4 km) northwest of Marion.

SR 203 traverses the northwestern portion of Delaware County and the southern half of Marion County.

There are no segments of SR 203 that are included within the National Highway System (NHS), a network of highways deemed to be most important for the economy, mobility and defense of the country.

[3][4] In 1938, SR 203 was extended north to its present terminus at what is now SR 309, but at the time a part of the now-defunct U.S. Route 30S (US 30S).