Kōsei (甲西町, Kōsei-chō) was a town located in Kōka District, Shiga Prefecture, Japan.

"Kōsei" means "western Kōka".

[1] As of 2003, the town had an estimated population of 42,471 and a density of 743.02 persons per km2.

On October 1, 2004, Kōsei merged with the town of Ishibe (also from Kōka District) to create the city of Konan.

[3] JR West – Kusatsu Line St. Johns, Michigan, United States.