9 U.S. counties with the strongest economic growth

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.

9. Santa Clara, California: 2.9 percent

This county of 1.7 million residents is home to Silicon Valley, known for fast-growing companies such as Apple (AAPL) and Google (GOOG). Technology will continue to fuel this county, but it also faces downsides, such as the high cost of housing.

"We do see demand for high-tech goods and services, so overall we are expecting economic output to be quite strong," Mowell said. "But in terms of the number of people continuing to move there, that's becoming increasingly difficult."

Over the next five years, the county's compound annual growth rate will be 2.9 percent, according to Oxford Economics.

8. Adams, Colorado: 2.9 percent

Home to Aurora and Arvada, the county of Adams serves as a suburban region for Denver. The county's compound annual growth rate will hit 2.9 percent over the next five years, Oxford Economics estimates.

That represents an upbeat view of Denver's economy, which will draw more workers and businesses into surrounding towns like those in Adams County.

7. Washington, Oregon: 3.1 percent

While Washington County, Oregon, might not be well-known, its largest city has sparked a TV show and pop culture references: Portland.

Leading the county's growth will be the economic strength of Portland and its suburbs.

"Oregon's economy is hitting the sweet spot, which only happens at or near full employment. Wages for workers are rising faster," wrote Josh Lehner, an economist in the Oregon's Office of Economic Analysis, in a blog post last month.

6. Fort Bend, Texas: 3.1 percent

This Houston-area county is projected to see compound annual growth of 3.1 percent, according to Oxford Economics. Its biggest city is Sugar Land, an affluent town that's also home to Imperial Sugar.

Housing development is growing in the county, partly as real estate has grown more expensive elsewhere, the Houston Chronicle noted in 2015. Fort Bend's population rose by 17 percent from 2010 to 2014.

5. San Francisco, California: 3.2 percent

San Francisco should see continued expansion from the tech industry, reaching compound annual growth of 3.2 percent over the next five years, Oxford Economics said. The city is home to tech businesses such as Twitter (TWTR) and Uber, as well as retailers such as Gap (GPS).

San Francisco has a problem, however: Sharply rising housing costs have made it unaffordable for many workers, and some residents are choosing to relocate outside the Bay Area as a result.

"You can earn $250,000 a year and live like a peasant," Mowell said. "The thing in the Bay Area now is dealing with basic tangible issues of where do we put these people."

4. Will, Illinois: 3.2 percent

This Chicago-area county, which includes parts of Joliet and Naperville, is something of an outlier because it has a relatively small economic base, Mowell said. The county is forecast to grow by 3.2 percent over the next five years on a compound annual growth rate.

Nevertheless, it's home to Citgo Lemont Refinery and Amazon (AMZN) warehouses. Amazon recently announced it would build another warehouse, of 440,000 square feet, there. The online retailer has become "the gift that keeps on giving" for the county, according to The Chicago Tribune.

3. Montgomery, Texas: 3.4 percent

With a compound annual growth rate of 3.4 percent, Montgomery County has a become a successful "edge city" for Houston, Mowell said.

The county is also home to The Woodlands, a master-planned community that was ranked as the sixth-best city to live in by Niche. The Woodlands is home to corporate offices for companies including Chevron Phillips and Anadarko (APC).

2. Collin, Texas: 4 percent

Collin County, Texas, in the Dallas-Forth Worth area, is projected to enjoy 4 percent compound annual growth rate over the next five years.

The county's economic base is expanding beyond traditional suburban industries like retail and into technology and professional services, Mowell said.

1. Denton, Texas: 4.1 percent

Denton County is forecast to experience the strongest economic growth over the next five years, at 4.1 percent. Home to parts of Dallas and Fort Worth, the county is experiencing population and economic growth, although on a smaller base than some of country's other top-growing regions.

Major employers in the county include University of North Texas and Walmart (WMT), as well as Peterbilt Motors (PCAR), which is located in the city of Denton.