From our friends at the Metro Chicago Information Center (MCIC):
The communities listed above have at least two things in common. One, they're all in Illinois and two, they all have new demographic, social, economic and housing data available for the first time since the 2000 decennial census!
The American Community Survey (ACS), conducted by the U.S. Census Bureau, is a nationwide survey of U.S. households that provides vital data and information on a "rolling" basis, rather than every ten years.