While younger workers still make up three-quarters of the nation’s workforce, a steady surge in the number of workers 55 and older accounts for all of the net increase in employment — about 17 million jobs — since 2000, according to a new analysis.

The nation’s 35.5 million older workers now make up 23.1 percent of the U.S. workforce of 154 million, according to William Emmons, lead economist with the Center for Household Financial Stability at the Federal Reserve Bank of St. Louis. That’s up significantly from 2000, when 18.4 million older workers accounted for just 13.4 percent of the working population, Emmons wrote in an article published online Jan. 15.

Employment among older workers grew at an even pace during the early and mid-2000s, to 26.2 million (17.9 percent of the workforce) in 2007, and then maintained that growth, even in the depths of the 2008-2009 downturn, when the nation’s economy shed millions of jobs.

Employment of younger workers, in contrast, dipped during the 2001-2002 recession. It recovered only slightly in the mid-2000s before taking a brutal hit during the late 2000s downturn, from which it has yet to fully recover. There were 118.5 million workers under age 55 in 2017, 1.5 million fewer than the high-water mark a decade earlier.

But the boom in older workers is expected to gradually diminish over the next two decades when more and more boomers and Gen Xers finally retire. By 2027, Emmons projects, 55-and-older workers will grow to 40 million and amount to 23.7 percent of the workforce. In the 10 years after that, their numbers will grow by just 300,000, and their percentage of the workforce will slip to 22.8 percent.