The U.S. Census Bureau is out with a new report on the state's most concentrated population areas. The fastest growing county in Tennessee from July 2012 to July 2013 was Williamson County, whose population grew three-point-one percent over the period. It was followed by Rutherford County, which grew by two-point-five percent in that statistical year. Wilson County grew by two-point-four percent, Maury County two-point-one percent and Sumner County by one-point-eight percent. Rutherford County grew by 6,925 people during this period. The information is based on annual population estimates complied by the U.S. Census Bureau.