New federal estimates for personal income at the county level suggest that the economy is improving in every county across Maine, albeit at a slower rate than the rest of the nation.

According to estimates released Thursday by the Bureau of Economic Analysis, the Greater Portland region, which includes Cumberland, York and Sagadahoc counties, remains Maine’s economic powerhouse, with nearly $26 billion in earnings in 2015 – nearly half of the entire state’s economy.

But Portland’s income growth from 2014 to 2015 underperformed that of most other metropolitan areas across the United States.

While the total income of all U.S. metro areas grew 4.7 percent between 2014 and 2015, the Portland region’s total income grew only 4.2 percent. Total income in both the Lewiston-Auburn metro area, which covers Androscoggin County, and in Greater Bangor, which covers Penobscot County, grew 3.4 percent.

The slower growth in the Bangor and Lewiston-Auburn regions is attributable, in part, to the bureau’s estimates of declining populations in those areas, which contributed to slower growth in total employment.

The lower earnings probably also reflect higher educational levels among workers in Portland and lower levels in Lewiston-Auburn and Bangor, said Yellow Light Breen, president and chief executive officer of the Maine Development Foundation.

“Maine’s biggest challenge has always been on productivity – we typically have been one of the worst in the country,” Breen said.

That doesn’t mean Mainers don’t work hard: Productivity often reflects the level of sophistication of a job or how well-equipped a factory is, which often require more education to operate. Without higher educational levels, Maine will continue to struggle on some economic measures, including incomes, Breen said.

He said the Portland region generally has more people with educations beyond high school than the state’s other two metro areas. Overall, about 43 percent of Mainers have continued their education beyond high school, Breen said, and his organization believes that figure should be at least 60 percent for the state to begin to see more economic progress.

On a per-capita basis, the Portland region’s average income per person in 2015 grew 3.7 percent over the year, to $49,246. The U.S. average was $48,112.

Among Maine’s 16 counties, income growth rates from 2014 to 2015 ranged from 2.4 percent in Aroostook County to 4.5 percent in Knox and York counties.