As of last month, it's the Chicago-Naperville-Joliet metropolitan area.
To reflect recent population trends, especially the growing size of the the nation's suburbs, the agencies altered the names of some of the country's 370 metropolitan statistical areas last month.
The names of the metropolitan areas change periodically. In 1990, the official name for the Chicago area was Chicago-Gary-Lake County.
By 1999, though, it was the Chicago-Gary-Kenosha metropolitan area, reflecting the population growth of some areas of southern Wisconsin.