America's cities have earned a reputation for drawing young workers and retirees, eager for short commutes and cosmopolitan life, but the suburbs may be ready for their prime time.

Millennials are starting to settle down and form families, which are prompting more of them to consider suburban life. At the same time, the high cost of living in some major cities means suburbia offers a more compelling argument for some workers and businesses.

Examining county-level data can help identify trends about growth and economic diversification, said Matthew Mowell, senior economist at Oxford Economics, which started forecasting county-level economic growth earlier this year.

Over the next five years, suburban counties are likely to have a greater share of millennials, which means the suburbs are likely to grow faster than the cores of metropolitan areas. Paying heed to such trends can help real estate investors and businesses make decisions about where to put their money.

"You see the nature of the economy changing," Mowell said. "When you're making a real estate play, you're trying to gauge what kind of cash flows are you going to see. When you buy a building, it's a localized decision, and having the county data can make a difference."

Six out of the nine counties forecast to have the strongest economic growth over the next five years are suburban. Two are considered core counties, or urban, while one is exurban.

Read on to learn about the nine counties Oxford Economics forecasts will show the strongest economic growth through 2022.