It’s been about ten years since the Great Recession officially ended in 2009. And by most measures, America’s economy is humming along at a pretty good clip.

But, as recent research by the Hamilton Project at the Brookings Institution demonstrates, not every part of the United States has shared equally in that return to prosperity.

In fact, nearly a decade after the Great Recession’s end, “prime-age employment rates are 16 percentage points lower in the bottom quintile of counties compared to those at the top. This gap is equivalent to bottom-quintile counties facing three Great Recession declines relative to top counties—a stark measure of the varying employment opportunities and outcomes that Americans face depending on their location,” researchers recently concluded.

An interactive map put together by the Hamilton Project allows users to track, down to the state and county level, how prosperity varies across the U.S. The map you see above is based on what the Hamilton Project describes as as a “Prosperity Index,” which combines such factors as a “county’s median household income, poverty rate, unemployment rate, prime-age employment rate, life expectancy, and housing vacancy rate.”

In the map at the top of this story, “blue counties have higher vitality scores and yellow counties have lower scores. The darker colored counties have higher populations,” researchers noted.

For this week’s edition of The Numbers Racket, we’re taking a dive into the Pennsylvania data to find the 10 most — and least — prosperous counties in the Keystone State.

The Top 10 Most Prosperous, based on their Prosperity Index Score:

Chester County: 1.6233 Montgomery County: 1.385 Bucks County: 1.2717 Cumberland County: 0.7063 Butler County: 0.6004 Adams County: 0.5412 Delaware County: 0.5122 Lancaster County: 0.4692 York County: 0.3855 Perry County: 0.3397

The Top 10 Least Prosperous, based on their Prosperity Index Score: