How many people live in Plymouth? It’s a question often asked, usually in relation to complaints about traffic, housing developments, and downtown parking.
No, the answer isn’t “too many.” Population figures are crucial. They’re used to calculate state and federal funding, grant applications, precinct maps, and how many representatives are looking out for Plymouth’s interests on Beacon Hill. They also determine the number of Congressional members dispatched to Washington. (Following the 2010 U.S. Census, the delegation was trimmed from 10 to 9.)
Despite reams of data and calculations, pinpointing Plymouth’s population is impossible. Thus, officials rely on carefully crafted estimates. That’s partly because the nationwide census takes place once every 10 years, with the next one set for 2030. Another reason: The town asks residents to self-report how many people are in a household. Some are reliably unreliable.
I started pondering Plymouth’s population after poring over the results of Tuesday’s election. With a small number of ballots remaining to be counted – including about 80 from overseas – 32,666 of the town’s 54,960 registered voters participated. Not a bad turnout.
But something seemed odd about the latter figure, so I dusted off my eighth-grade math skills and made a few calculations. The U.S. Census Bureau estimated Plymouth had 67,846 residents as of July 1, 2025. Subtracting the number of registered voters from that figure leaves just 12,886 people under the age of 18.
It seemed like a significant undercount. I’m pretty sure I saw more kids on bikes harassing motorists during the summer. So I turned to an expert – Town Clerk Kelly McElreath. She was still recovering from a marathon election day when we spoke Thursday.
First, she said, the number of registered voters is a fairly accurate tally of how many adults have a Plymouth address.
“I can tell you that there aren’t many people over the age of 18 that are not registered to vote,” McElreath said. That’s because of a 2023 state rule change that automatically adds people to voting rolls when they apply for or renew a driver’s license, learner’s permit, state I.D, MassHealth benefits, or an insurance plan through the Massachusetts Health Connector portal.
“I would love to say that I have the data that shows the exact census number,” she said. “We send out the annual street listing, also known as the town census, every year, and we don’t always get participation in that. I’ve been trying really hard to push the street listing to make sure everyone fills it out. We’re getting a little bit better with people returning it. But at the same time, they might not add their children onto it. They don’t put that they have three kids and give us that information.”
Since kids are people, too, that means the total count is likely higher than 67,846.
But there’s another complication – “inactive” voters. They include “people that have moved out of town and have not not returned their [town] census and have not participated in a state or a federal election in four years,” McElreath explained.
In 2025 alone, the town “inactivated” 21,000 voters who failed to fill out a town census, she said. That doesn’t necessarily mean they no longer live in Plymouth – though many likely don’t – and it doesn’t prevent those who still call the town home from showing up at a polling place with identification and getting reactivated.
Ultimately, McElreath said, the population is “definitely underreported.” By how much is unclear. We won’t have a better idea until the 2030 federal census figures are tabulated, but she did not disagree when I suggested the town has more than 70,000 residents, who – according to Facebook posters – on any given day are all looking for parking spaces on Main and Court streets.
“It’s not an exact science by any stretch of the imagination,” McElreath said. “You’re capturing as much [data] as you can.”
For those keeping score, the 2025 Census estimate of nearly 68,000 represents a 10.8% jump over a five-year period. That makes Plymouth one of the fastest growing communities in the state, but the increase pales in comparison with population booms of earlier decades, when the Pilgrim nuclear power plant kept taxes low and three-bedroom Capes were sprouting like an invasive species. The apex was between 1970 and 1980, when the population nearly doubled – from 18,606 to 35,913.
Even as she catches up on sleep this week, McElreath and other town employees already are preparing to send out the next town census in January. She urges people to not only to fill out and return the form, but also to list that slow-to-launch adult child who moved back home, or the newborn who’s keeping mom and dad up all night.
“If you had a baby in July, then you should be putting it on the census form the following January,” McElreath said. “It helps make the count as accurate as possible, and that matters.”
Mark Pothier can be reached at mark@plymouthindependent.org.