Complex sentence: The effects of the Great Recession slowed Rockford's population growth due to its proximity to Chicago; in 2006 alone, Rockford's metropolitan area rose in population by 1.6 percent, but since 2008, it has only declined.
Split into simpler sentences: The effects of the Great Recession slowed Rockford's population growth due to its proximity to Chicago. While in 2006 alone, Rockford's metropolitan area rose in population by 1.6 percent, since 2008 it has only declined.