Trinity County is a county located in the northwestern portion of the U.S. state of California. As of the 2010 census, the population was 13,786, making it the fourth-least populous county in California. The county seat and largest community is Weaverville.Trinity County is rugged, mountainous, heavily forested, and lies along the Trinity River within the Salmon/Klamath Mountains. The county has no traffic lights, no freeways, no parking meters, or no incorporated cities.