Sleep medicine deals with the causes, diagnosis and treatment of sleep disorders. A sleep medicine physician treats problems such as sleep apnea and snoring, insomnia and narcolepsy. Sleep apnea is when a person actually stops breathing for a few seconds during sleep, and is usually accompanied by loud snoring. Narcolepsy is a disorder of the central nervous system, and is characterized by excessive daytime sleepiness, and a tendency to sleep at inappropriate times, even if the person gets adequate nighttime sleep. Also considered sleep disorders are periodic limb movements and restless legs.

Treatment includes overnight study in a sleep center, where technicians observe, monitor, and analyze brain activity, respiratory function, muscle function and other variables that help diagnose complex sleep disorders. Sometimes a physician may fit a patient may with a device to measure a person's activity, their environmental temperature, light levels and mood state, all recorded by a computer the size of wrist watch. This allows the physician to get objective, accurate data on the patient's daily life, and help to assess sleep problems.

Doctor density varies by specialty and location. Illinois has 60 practicing sleep medicine doctors. Broken out by city, sleep medicine doctor density in Arlington Heights is 1, in Aurora is 1, in Belleville is 3, in Berwyn is 1, in Bloomington is 1, in Breese is 3, in Buffalo Grove is 2, in Chicago is 18, in Deerfield is 1, in Dekalb is 1, in Des Plaines is 2, in Downers Grove is 2, in Elgin is 1, in Elk Grove Village is 2, in Elmhurst is 1, in Evanston is 4, in Evergreen Park is 1, in Glenview is 2, in Hinsdale is 2, in Joliet is 3, in Lombard is 5, in Maryville is 1, in Mattoon is 1, in Maywood is 3, in Melrose Park is 2, in Mount Carmel is 1, in Murphysboro is 2, in Naperville is 3, in Normal is 2, in Oak Lawn is 1, in Oak Park is 1, in Oakbrook Terrace is 1, in Orland Park is 1, in Palatine is 1, in Park Ridge is 4, in Peoria is 1, in Rockford is 1, in Schaumburg is 1, in Silvis is 1, in Skokie is 3, in Sparta is 2, in Sterling is 1, in Urbana is 2, in Vernon Hills is 1, in Villa Park is 2, in Wheaton is 4, and in Winfield is 3.

Most people think that Chicago, because of its size and popularity, is Illinois’ capital city, but that distinction belongs to Springfield, home of the Abraham Lincoln Museum. Illinois has hundreds of museums, numerous yearly art and ethnic festivals, a lakeshore bordering Lake Michigan, and the many national forests and parks that offers visitors camping, horseback riding, biking, kayaking, and fishing. Chicago is home to the Sears Tower, the Shedd Aquarium, the Art Institute of Chicago, the Adler Planetarium, the Museum of Science and Industry, and other cultural opportunities and restaurants in the Navy Pier area.

According to 2005 Census estimates, Illinois has a population of 12,763,371. Of this population, 3,172,677 are under the age of 18 and 1,523,937 are at or above the age of 65.