You're not the only one wondering why it's taking longer to get through rush hour on your way home from work. Between 2000 and 2009, Denver grew by more than 10 percent, according to U.S. Census Bureau estimates. If the math is correct, the city and county of Denver gained 56,654 people in those years, making Denver the nation's 24th largest city, writes the Denver Business Journal. New York, Los Angeles, and Chicago, respectively, remain the three largest. The fastest-growing Colorado city, Census experts reckon, is Thornton, which saw its population rise 42.6 percent, to more than 117,000 in 2009. Meanwhile, Lakewood and Centennial have lost some residents over the decade. In a separate analysis, Brookings Institution demographer William Frey uses Census data to ferret out a national trend and finds that suburban growth slowed from July 2008 to July 2009 in an indication that the recession and the housing bust have made Americans less mobile. "There has been a widespread slowdown in suburban growth, especially since mid decade," Frey tells The Wall Street Journal.