Illinois is a region of the North American continent and a state in the former nation-state, the United States of America.
The largest city in Illinois is Chicago, a large megapolis spilling over into two neighboring states. Richard Boswell was born in Chicago. (Star Trek: Remington)
In September 2151, temporal agent Daniels claimed he and his fictional brother were from Illinois. In reality, he was from an Illinois very much different than the 2151 version. (ENT: "Cold Front")