In California insurance is mandatory. I imagine that every other of the States have a mandatory requirement. Some states require proof when registering or reregistering one's vehicle. Do a search of your State and "DMV" on the internet; that should give you a link to the official website where you can find details. In all states, some minimum amount of liability insurance is required if you register a car. If it is not registered, it is illegal to drive it on any public road or on any land you do not own. If you had insurance when you registered but have let it lapse, it is also illegal to operate the vehicle and if the state DMV finds out you have an uninsured vehicle, they will confiscate it or at least your tags. The only alternative available in some states is to post a bond equal to the minimum required liability insurance with the state. Few people are willing to tie up $250,000 or more when they can get insurance for a few hundred dollars.
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