Is it legal to have an uninsured car in your driveway?

It will differ from state to state, but some states it is illegal.

If it's your land, then there should be no problem. If your driveway is on rented land, meaning you don't own it, you need to get the permission of the landloard/landowner.

It would be advisable though to carry the barest minimum of insurance, just in case a hail storm damages the vehicle, or a tree branch hits it, or the neighborhood kid rams it with his bike or wagon.