Glenn County was formed in 1891 from parts of Colusa County. The county was named after prominent citizen Hugh J. Glenn, who was the state's largest wheat farmer at the time. Today the county remains an agricultural area, with a population of just 29,000 operating nearly 1200 farms that produce rice, almonds, milk products, prunes and livestock.
- 1 Tehama County
- 2 Butte County
- 3 Colusa County - Located south of Glenn County, visitors to rural Colusa County will find an abundance of rice fields and almond trees, but a limited number of amenities and attractions. Sights that may be of interest include four national wildlife refuges, as well as the Colusa County Courthouse in the town of Colusa, which was erected in 1861 and is the oldest remaining courthouse in the Sacramento Valley.
- 4 Lake County - Rural Lake County lies southwest of Glenn County and is named after Clear Lake, a body of water that is believed to be 2.5 million years old and thus the oldest lake in North America. The lake is sometimes called the "Bass Capital of the West", and its 100 miles of shoreline offer ample opportunity for fishing, boating, swimming and birdwatching. The county is also home to the Clear Lake Volcanic Field, a region that includes lava domes, cinder cones, the 4,305 foot tall volcano Mount Konocti, and the world's largest geothermal field with more than twenty geothermal power plants.
- 5 Mendocino County