Ruiru is a municipality and sub-county located in the Kiambu County region of Kenya. It is situated within the greater Nairobi Metropolitan region and serves as a significant urban center for the area.
According to the 2019 national population census, Ruiru was ranked as the fourth largest urban center in Kenya by population. The name of the municipality is derived from Kikuyu origin and may be related to the black cotton soil found throughout most parts of the region.