It comprises of the two administrative Counties of Machakos and Makueni. The Diocese headquarters are situated in Machakos town, about 70 kilometers east of Nairobi City. The Diocese covers an estimated area of 15,183 Sq. Kilometers comprising 13 Deaneries, 72 Parishes and about 13,200 Outstations.
When the Catholic Diocese of Machakos was created from the Archdiocese of Nairobi on May 29th, 1969, Imeritus Bishop, Rt. Rev. Raphael S. Ndingi Mwana-a-Nzeki became the first bishop and reigned in the period 7th September, 1969 to 1st January, 1972. The late Bishop, Rt. Rev. Urbanus Joseph Kioko took over as the Second Bishop for the period 20th July, 1973 to 15th March, 2003 and was succeeded by Rt. Rev. Martin Kivuva Musonde as the third Bishop from the 15th March, 2003. Currently, the Diocese is blessed with 158 Diocesan Priests and 27 Missionary Priests from different orders, 188 Catholic Nuns (Sisters) from different Congregations, 41 Brothers of St. Peter Clever and, about 1,630 Catechists.
The population within the jurisdiction of the Catholic Diocese of Machakos, mainly the Akamba, was estimated at 2,544,641, of whom 1,134,699 were Catholics as at 31st December, 2011. Besides the Akamba, there are pockets of other communities concentrated mainly in towns and new settlements.