It is one of four constituencies of Nyamira County.
Prior to 2013, West Mugirango Constituency had twelve wards: Kebirigo, Nyamira, Rangenyo, Sironga, part of Bogichora, part of Bonyamatuta, Gesiaga, Keera, Miruka-Nyamaiya, Motagara and Sironga.
[2] However, ward boundaries and some of the names were revised to five, namely: Bogichora, Bonyamatuta, Bosamaro, Nyamaiya and Township.
[3] Nyamira South Sub-county shares common boundaries with West Mugirango Constituency.
The Sub-county is headed by the sub-county administrator, appointed by a County Public Service Board.