Kōsei, Shiga

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

As of 2003, the town had an estimated population of 42,471 and a density of 743.02 persons per km². The total area was 57.16 km².

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

Its sister city was St. Johns, Michigan in United States.