Brentwood

St. Charles County.

Population: 84,009.

St. Charles County. Population 84,009. O’Fallon is the largest municipality in St. Charles County and is ranked by Money Magazine as one of the “Best 100 Places to Live.” O’Fallon experienced a boom in the 1990’s with an increase in jobs, influx of residents, infrastructure improvements, and retail and manufacturing growth. The town is a popular tourist attraction with several early American history sites.