Chicago has biggest population dip as southern states grow

A Chicago Transit Authority Green Line train travels West away from downtown Chicago, Thursday, March 23, 2017, in Chicago. Census data shows the Chicago region has lost more residents than any other U.S. metropolitan area, a drop that comes as other Midwestern cities lost population and South and Southwest parts of the country saw gains. (AP Photo/Charles Rex Arbogast) (The Associated Press)

A Chicago Transit Authority Green Line train travels West away from downtown Chicago, Thursday, March 23, 2017, in Chicago. Chicago had the biggest population drop among major metropolitan areas, according to new Census data, part of a years-long decline for the region. (AP Photo/Charles Rex Arbogast) (The Associated Press)

Census data show the Chicago region lost more residents than any other U.S. metropolitan area last year, a drop coinciding with other Midwestern cities experiencing declines as the South and Southwest regions saw gains.

Two Texas metropolitan areas surrounding Dallas and Houston reported the biggest numeric increases between July 2015 and July 2016.

Experts say the reasons for the shifts are complex.

Some families cite concerns about crime and schools. While demographers say the bigger picture from Thursday's data could be the reanimation of a trend that paused during the recession — of Americans on the move from the Snow Belt to the suburbs of big cities, and to the Sun Belt.

Illinois' Cook County had the biggest annual population drop while Arizona's Maricopa County had the highest.