Trans-Nzoia County  is a county in the former Rift Valley Province, Kenya, located between the Nzoia River and Mount Elgon, 380 km northwest of Nairobi. At its centre is the town of Kitale which is the capital and largest town. The county borders Bungoma to the west, Uasin Gishu and Kakamega to the south, Elgeyo-Marakwet to the east, West Pokot to the north and the republic of Uganda to the Northwest. Trans Nzoia covers an area of 2495.5 square kilometres.

Historically the area has been inhabited by the sabaot people. After independence many of the farms vacated by white settlers were bought by individuals from other ethnic groups in Kenya. Kitale, its capital town, is now majorly luhya with inhabits from other tribes in Kenya occupying almost less than 1% of the population.

The county is largely agricultural with both large scale and small scale wheat, maize and dairy farming. The county is referred to as the basket of Kenya for its role in food production in the country. The majority of its inhabitants are however generally poor.