The county of Kisumu is one of the three cities-counties of Kenya, the other two are Nairobi and Mombasa. In total, there are 47 counties in Kenya. Its borders follow those of the original district of Kisumu, one of the former administrative districts of the former Nyanza province in western Kenya. Its capital is the city of Kisumu. It has a population of 968.909. The land area of Kisumu County totals 2,085.9 km². The neighbors of Kisumu County are Siaya County to the west, Vihiga County to the north, Nandi County to the northeast and Kericho County to the east. Its neighbor to the south is the county of Nyamira and the county of Homa Bay is to the southwest.
The county has a coast on Lake Victoria, occupying the north, the west and a part of the southern coasts of the Gulf of Winam.