Kisumu is a port city in western Kenya at 1,131 m (3,711 ft), with a population of 355,024 (1999 census). It is the third largest city in Kenya, the principal city of western Kenya, the immediate former capital of Nyanza Province and the headquarters of Kisumu County. It has a municipal charter but no city charter. It is the largest city in Nyanza region and second most important city after Kampala in the greater Lake Victoria basin.

The port was founded in 1901 as the main inland terminal of the Uganda Railway and named Port Florence. Although trade stagnated in the 1980s and 1990s, it is again growing around oil exports.

Kisumu literally means a place of barter trade "sumo". The city has "Friendship" status with Cheltenham, UK and "sister city" status with Roanoke, Virginia and Boulder, Colorado, USA.

Kisumu was identified by the British explorers in early 1898 as an alternative railway terminus and port for the Uganda railway, then under construction. It was to replace Port Victoria, then an important centre on the caravan trade route, near the delta of River Nzoia. Kisumu was ideally located on the shores of Lake Victoria at the cusp of the Winam Gulf, at the end of the caravan trail from Pemba, Mombasa, Malindi and had the potential for connection to the whole of the Lake region by steamers. In July 1899, the first skeleton plan for Kisumu was prepared. This included landing places and wharves along the northern lake shore, near the present day Airport Road. Demarcations for Government buildings and retail shops were also included in the plan.