<Tr> <Th> Summer (DST) </Th> <Td> CDT (UTC - 5) </Td> </Tr> <Tr> <Th> Area codes </Th> <Td> 219, 224 / 847, 262, 312 / 872, 331 / 630, 574, 708, 773 / 872 and 779 / 815 </Td> </Tr> <P> The Chicago metropolitan area, or Chicagoland, is the metropolitan area that includes the city of Chicago, Illinois, and its suburbs . With an estimated population of 9.4 million people, it is the third largest metropolitan area in the United States . </P> <P> The Chicago metropolitan area is one of the world's largest and most diversified economies, with more than four million employees and generating an annual gross regional product (GRP) of over $561 billion . The region is home to more than 400 major corporate headquarters, including 31 in the Fortune 500 . </P>

What's the population of the greater chicago area