- Ukiah is a city located in Mendocino County, California, United States. It is the county seat and largest city of Mendocino County. The city is known for its natural beauty, including nearby redwood forests, vineyards, and the Ukiah Valley. It has a population of approximately 16,000 people. Ukiah offers various recreational activities, cultural events, and a charming downtown area with shops and restaurants. The city is also home to Ukiah High School and Mendocino College.