The web site is trustworthy. Cannot say the same for the organization behind it :-(
Be careful of doing business with the State of Illinois - they have driven many, many small businesses out of business by not paying in a timely manner. There has been much recent publicity on this. But this practice, and the resulting bankruptcies, has been going on for years and years.
The official website of the State of Illinois is the gateway to services and information about living, visiting, business, working, health and wellness, learning, education, facts, public safety, technology, and government in Illinois.