Chesterfield is a second-ring western suburb of St. Louis and is the largest city in west St. Louis County, Missouri, United States. As of the 2010 census the population is 47,484 which is the 14th largest city in Missouri. Chesterfield celebrated the 20th anniversary of its founding in 2008. Chesterfield is the home of the headquarters of the Reinsurance Group of America (RGA), and as of 2013-14 has been experiencing a mass-construction boom. Two outlet malls have recently completed construction in the Valley.