More empty nesters and twentysomethings are living in the District and are largely responsible for the city’s first population boom in 50 years, new census data show. Meanwhile, the number of school-age children has dropped and those in their late 30s and early 40s have declined as families move out of the city.

The phenomenon is a national trend following the rise of cities over the last decade as massive revitalization efforts have attracted young professionals starting out and baby boomers who want to downsize, said Benjamin Orr, a Brookings Institution analyst.