Is Illinois part of the US?

Yes, Illinois is a state in the United States. It is located in the Midwest region of the country and borders Indiana to the east, Kentucky to the southeast, Missouri to the west, Iowa and Wisconsin to the northwest, and Lake Michigan to the northeast. Illinois is the 25th most populous state in the US, with a population of approximately 12.7 million people. The capital of Illinois is Springfield, and its largest city is Chicago.