It's a legacy category of company that gets favorable regulatory treatment (mostly in the form of more flexible pricing) for auto insurance policies written in the state of Texas. It's been illegal to form a new Texas county mutual since 1955, but the ~20 that have remained in existence since that time are still grandfathered in. Some of them have been acquired by big national insurers (e.g., GEICO fully owns one and has a controlling interest in at least one other), which issue policies on the county mutuals' paper and then cede (transfer) the business back to the parent company. Other county mutuals effectively license their favorable regulatory treatment to other, unaffiliated insurance companies. A significant minority of the auto insurance policies issued in Texas today are still issued on county mutuals' paper.