Isiolo County is a county in the former Eastern Province of Kenya. Its population is 268,002 (2019 census) and its capital and largest city is Isiolo. Isiolo is also the Least Populated County in Kenya. Isiolo County is to be the first county to be developed as part of the Kenya Vision 2030 program. Other upcoming urban centres are: Garbatulla, Modogashe, Kinna, Merti and Oldonyiro.
The local topography is arid or semi-arid low plains. Ewaso Nyiro River flows through the county and partly bounds it. It borders Marsabit County to the north, Wajir County to the east, Garissa and Tana River counties to the south east, Meru County to the south, Laikipia County to the south west and Samburu County to the west.