The Kisii (also known as AbaGusii, as they prefer to call themselves) is a community of Bantu speakers who inhabit the two counties (Kisii, formerly Kisii District and Nyamira) in Nyanza Province, Western Kenya. Gusii is the fond reference to their homeland and Mogusii is culturally identified as their founder and patriarch.

Kisii town - known as Bosongo by the locals - is located in Nyanza Province to the southwest of Kenya and is home to the Gusii people. The name Bosongo is believed to have originated from Abasongo (to mean the Whites) who lived in the town during the colonial times. According to the 1979 census, Kisii District had a population of 588,000. The AbaGusii increased to 2.2 million in the latest Kenya Census 2009.

The Abagusii, like the Abaluyia (Luhya), claim to have come from areas further north. As these Bantu speakers migrated from the Congo, they split up into different groups with the Kisii ending up in Nyanza Province near Lake Victoria. (The Kikuyu, Kamba, and other groups in Kenya continued the hunt for richer soil for farming and moved on eastwards across the Rift valley to their current locations. They later settled in the now-called Central and Rift Valley Provinces of Kenya.)