Its eastern terminus is at a signalized intersection with SR 204 in the central business district of the village of Thornville.

SR 188 traverses the eastern part of Pickaway County, then through the western, central and northeastern portions of Fairfield County and finally the northwestern corner of Perry County.

No segment of SR 188 is included as a part of the National Highway System (NHS).

The NHS is a network of routes deemed to be most important for the economy, mobility and defense of the nation.

[4][5] In 1937, SR 188 was extended to the northeast from Lancaster along what was at the time an un-numbered roadway to its current eastern terminus at SR 204 in Thornville.