ST. CHARLES COUNTY, Mo. – The Greater St. Louis Metropolitan Area’s population hasn’t changed much in recent history, but it’s consistently experienced two big demographic changes for decades.

People keep moving away from the City of St. Louis. People keep moving to St. Charles County.

A recent FOX 2 analysis revealed that St. Louis City has lost around half of its population over the past half-century, while St. Charles County has more than tripled in size during the same time frame.

That doesn’t mean each outbound move from St. Louis is directly related to each inbound move to St. Charles County, but the region’s largely unchanged size seems to support the concept of westward expansion.

Census data trends show that St. Charles County passed St. Louis City in size at some point in the early 2000s. In the present day, St. Charles County has about 100,000 more residents than the City of St. Louis, all while St. Louis County, sandwiched in between both, hasn’t seen much change.

Where has St. Charles County grown most over the past decade? The further west you go, the more likely you’ll see its biggest points of growth.

According to U.S. Census figures, from 2010 to 2020, the city of Wentzville led all county municipalities in total population growth. It added more than 15,000 people, increasing more than 50% over the course of a decade.

In terms of percentage growth, during that same timeframe, the town of Flint Hill grew the fastest. It nearly doubled in population from 2010 to 2020, and with an 87% growth clip, it’s now home to around 1,000 residents.

Wentzville and Flint Hill are both located within minutes of Foristell, the last incorporated municipality along Interstate 70 before drivers head into Warren County. The city of Foristell is a rather small and rural community, but it too has grown roughly 10% in size over the last decade.

As for total population growth, O’Fallon added the second-most people after Wentzville over the past decade. The city of O’Fallon increased by roughly 12,000 people, or 15%, from 2010 to 2020. It is also one of the more western municipalities of St. Charles County.

Second in percentage growth, from 2010 to 2020, was the city of Cottleville. It grew 82% over the course of a decade, adding around 2,500 new people.

An analysis from St. Charles County projects the population of St. Charles County could reach 470,000 people by the start of 2030. The county has been adding tens of thousands of new residents consistently each decade since the start of the 1960s.