Insurance companies. Car insurance companies register themselves with the illinois department of insurance. These factors include your credit score, the type of car you drive, how many years of driving experience you have, and even where you live in illinois. A poor credit score can exponentially increase the cost of car insurance in illinois. Lower than the national average auto insurance premium, and illinois ranks 25 out of 50 for the most affordable car insurance rates in the u. This information may be different than what you see when you visit an insurance provider, insurance agency, or insurance company website. Some cities in illinois have cheaper car insurance premiums than others because insurance companies take a driver's zip code into account when calculating their premium, alongside other factors.