Glenn County is a county located in the U.S. state of California. As of the 2020 census, the population was 28,917. The county seat is Willows. It is located in the Sacramento Valley, in the northern part of the California Central Valley. The Grindstone Rancheria, reservation of the Grindstone Indian Rancheria of Wintun-Wailaki Indians, is located in Glenn County.