Kiambu County is a county in the former Central Province of Kenya. Its capital is Kiambu and its largest town is Thika town. Kiambu County is the second most populous county in Kenya after Nairobi County. Kiambu County borders Nairobi and Kajiado Counties to the South, Machakos to the East, Murang'a to the North and North East, Nyandarua to the North West, and Nakuru to the West. It has a population of 2,417,735.

Machakos County is one of the 47 counties of Kenya, which came into being because of the devolved system of governance occasioned by the 2010 constitution of Kenya. The country's first administrative headquarters are in Machakos Town, which is the largest town in the county. The county had a population of 1,421,932 as of 2019. The county borders Nairobi and Kiambu counties to the west, Embu to the north, Kitui to the east, Makueni to the south, Kajiado to the south west, and Muranga and Kirinyaga to the north west.