Kitui County is one of the 47 counties of Kenya in the former Eastern Province of Kenya. Its capital and largest town is Kitui. Mwingi is also another major urban centre. The county has a population of about 1.2 million people (as of 2024) and an area of 30,496 km². It lies between latitudes 0°10 South and 3°0 South and longitudes 37°50 East and 39°0 East.

Kitui County shares its borders with seven counties; Tharaka-Nithi and Meru to the north, Embu to the northwest, Machakos and Makueni to the west, Tana River to the east and southeast, and Taita-Taveta to the south.

Kitui County is "representative" of the fragile Arid and Semi-arid lands of Kenya that account for 80 percent of the land mass. These lands are characterized by high poverty levels, agro-pastoral livelihoods, high vulnerability to climate shocks, underdeveloped social infrastructure, low access to social services, and in extreme cases conflict over natural resources, especially during droughts".

The name Kitui means 'a place where iron goods are made'. The Kamba iron-smiths who settled in the county many years before the colonial period are the ones who named the area Kitui.

Kitui County has a total population of 1.2 million people (as of 2024). In comparison, in 2009 the population was 1,136,187 people.

Data from 2019 indicated that there are 262,942 households with an average household size of 4.3 persons per household, and a population density of 37 people per square kilometre.

The population is mostly made up of people of the Akamba ethnicity. Tharaka people, a section of the Ameru, are also found in Kitui County mainly in Tharaka ward. There is also a growing Somali presence.

There are eight sub counties, forty county assembly wards, one hundred and sixty seven locations and four hundred and eleven sub-locations.