Marsabit County is located in the extreme part of northern Kenya and has a total area of 70,961.2 sq. km. It has an international boundary with Ethiopia to the north, borders Turkana County to the west, Samburu County to the south and Wajir and Isiolo counties to the east. It lies between latitude 02° 45° North and 04° 27° North and longitude 37° 57° East and 39° 21° East.
Most of the county constitutes an extensive plain lying between 300m and 900m above sea level, sloping gently towards the south east. The plain is bordered to the west and north by hills and mountain ranges and is broken by volcanic cones and calderas. The most notable topographical features of the county are Ol Donyo Ranges (2,066m above sea level) in the south west, Mt. Marsabit (1,865m above sea level) in the central part of the county, Hurri Hills (1,685m above sea level) in the north eastern part of the county, Mt. Kulal (2,235m above sea level) in the north west and the mountains around Sololo-Moyale escarpment (up to 1,400m above sea level) in the north east. The main physical feature is the Chalbi Desert which forms a large depression covering an area of 948 sq km, lying between 435 and 500m elevation. The depression is within the Great Rift Valley and is separated from Lake Turkana, which is 65 -100m lower in elevation, by a ridge that rises to 700m.