What does 4 pCi/L mean?
4 pCi/L is the action level EPA set for indoor radon. Picocuries per liter is a measure of radon in air. It is not a score your county assigns to your house.
The Minnesota Department of Health says any radon level carries some risk, and that you cannot get radon all the way to zero. MDH recommends a mitigation system at 4 pCi/L or higher. Between 2 and 4 pCi/L, MDH says a system can be considered so you can get the level lower.
EPA's zone map uses 4 pCi/L as the line for its highest potential category. Zone 1 means the predicted average indoor screening level may be greater than 4 pCi/L. Zone 2 may fall between 2 and 4. Zone 3 may be lower than 2. EPA still says every home should be tested, including homes in Zone 3.
A zone is a planning tool for governments. Your test kit or monitor is the number that belongs to your home. If you have not tested, you do not know yet.
Next: what to do with a result, or find a local kit.