The district was adjacent to the northern border of Nairobi and had a population of 744,010.
[1] Created during the colonial era, it underwent changes, absorbing part of Thika District, losing some of its regions to Nairobi such as Dagoretti while gaining some including Ruiru.
In 2009, Thika District was declared unlawfully created and was reabsorbed to Kiambu yet again.
In 2013, Kiambu County was effected on the same boundaries as the district absorbing it in the process.
The district was predominantly rural, but its urban population is increasing as Nairobi is growing rapidly.