State population growth is forecast to slow

The population of Massachusetts will grow dramatically older over the next two decades, with 1 in 5 residents age 65 and older by 2030, according to a new demographic forecast.

The state’s overall population is expected to grow much more slowly than the rest of the nation during that period, threatening to dilute further the Bay State’s political clout in Washington. The University of Massachusetts study pegs the state population growth at 4.4 percent between 2010 and 2030, while the country as a whole is expected to grow by 15.6 percent.

As it shrinks in proportion to the rest of the United States, Massachusetts will grow older. In 2010, about 14 percent of the state’s population was 65 and over. Produced by the University of Massachusetts Donahue Institute, the study projects the state population age 19 and under will decrease, from 25 percent of the population in 2010 to 22 percent by 2030.

The graying of the state will probably have major policy implications for Beacon Hill, with challenges to health care and pension systems.

Estimates from the University of Virginia, released earlier this year, pin the national share of the population over age 65 at 18.4 percent by 2030, putting Massachusetts well above the country’s average.

Massachusetts is expected to add nearly 291,000 residents over the 20-year window, bringing its headcount to 6,838,254. The vast majority of that growth is projected to come by 2020. Between 2000 and 2010, the nation as a whole added residents at a 9.7 percent clip, while the state’s rate was just 3.1 percent.

The sluggish overall growth could reduce the size of the congressional delegation. Congressional apportionment is recalculated every 10 years, and Massachusetts lost seats after the 1990 and 2010 tabulations.

Greater Boston, the western suburbs, and central regions are expected to add residents, while the lower Pioneer Valley is projected to contract, and the Franklin and Berkshire regions are on pace to register barely detectable growth.