A U.S. Census survey showed 11 cities and towns west of the Mississippi were some of the fastest growing in the nation — and two are in Arizona.

Of the 15 fastest growing cities in the country, Goodyear ranked 14 and Buckeye was 15. Both West Valley towns saw their populations increase by more than 4 percent between July 2014 and 2015.

"And for Maricopa County we see that it’s adding people due to high natural increase so there’s more births than deaths; also, there are more people moving into Maricopa County than out of it," said Census demographer Sarah Gibb.

Gibb said most of the fastest growing cities were in the South and West. Texas was home to five, while Utah, Colorado and California all had at least one city make the cut.

Phoenix also saw a spike in its population, though it continues to rank number six on the list of most populous cities, just behind Philadelphia.

10 Most Populated Cities In The United States

Based on 2015 population estimate from U.S. Census Bureau.