The preliminary unemployment rate for March is the lowest since 1976, when current record-keeping began.

Glenn Mills, chief economist with the Maine Department of Labor, said the rate of 2.7 percent could be the lowest since 1957, when President Dwight Eisenhower was in the White House.

Mills didn’t have monthly estimates for the years before 1976, but based on annual averages and other records of the 1950s, ’60s and early ’70s, he arrived at an educated guess of 1957.

The state’s monthly unemployment rate continues a streak of 28 consecutive months where rates have been below 4 percent. Such persistent low unemployment has been contributing to a tightening labor pool.

“This is (a) continuation of the ongoing trend of an improving economy as well as demographic constraints that are causing a tightening of the labor market,” Mills said.

March’s rate is down slightly from February’s 2.9 percent, and well below March 2017’s rate of 3.3 percent.

The U.S. preliminary unemployment rate of 4.1 percent for March has been unchanged for six months; it is down from 4.7 percent one year ago. The New England average was 3.6 percent.

Mills said efforts already are underway, both in government and the private sector, to attract workers.

“There has been an improvement in migration patterns to Maine where we’re drawing some working-age people back,” he said. “That will help alleviate some of the tightness. But each year we move forward, we have more (people) moving into retirement, so the balance of that is something we’re going to have to sit back and watch.

“If there is not enough migration to offset people who leave the labor force, I think you’ll see more marketing efforts.”

The unemployment rate does not capture people who have stopped looking for work, but Mills said economists use other metrics to measure labor underutilization. He said those measures also show a record-low amount of people out of work.

Mills also said people sometimes forget when looking at the unemployment rate that there is a difference between not being employed and being unemployed.

Last year, 62 percent of Mainers over the age of 16 were employed, which left 38 percent not employed. The overwhelming majority of that group were retired, home caring for children or other family members, in school, or not seeking work for other reasons.