TRUMBULL — When Democrats swept nearly all the municipal races last year, their electoral wins were at least partly attributable to a registered voter advantage that had grown by more than 2 percent.

Democrats had grown by 565 voters to 7,227 Democrats compared with 6,662 Republicans. That’s the widest margin either party had held in more than a decade and was the culmination of a four-year trend.

Now, that advantage has nearly doubled and shows no sign of slowing.

“This is part of a trend, what you’re seeing in Trumbull and across Fairfield County and nationally across the suburbs,” Trumbull Democratic Chairman Tom Kelly said. “This is the result of some very active, energized local Democratic parties really working hard.”

According to the Trumbull Registrar of Voters office, the registered voter advantage for Democrats has climbed to more than 1,000. Of the 26,820 registered voters in Trumbull, 7,692 of them (28.6 percent) are now affiliated with the Democratic Party.

There are 6,613 registered Republicans in town (24.6 percent). The largest group remains the unaffiliated voters at 12,202 (45.5 percent). There are 313 Trumbull voters registered with a minor party, including the Green, Independent, Libertarian and Working Families parties.

To put that number in perspective, Trumbull has added 799 registered voters in the past year. The Democratic Party has grown by 465, while the GOP has decreased by 49 voters.

Republican Town Chairman Chris Bandecchi and GOP Registrar of Voters William Holden did not return messages requesting comment.

Taken by itself, the party registration numbers are no guarantee of success. Former First Selectman Timothy Herbst, a Republican, soundly defeated four-term Democratic incumbent Ray Baldwin in 2009 despite Democrats holding a 423-voter edge (about 1.7 percentage points).

During Herbst’s four terms in office, the Democratic voter edge gradually eroded until 2014 when there were 41 more Republicans than Democrats in town. The following year, when Herbst won a narrow race against Vicki Tesoro, that gap had grown slightly to 73 — 6,093 to 6,020.

In 2016, driven by a surge in voter registrations, the Democrats regained the advantage at 7,016 to 6,834.

This year, there are no municipal races on the ballot. But there are three Town Charter revision questions, including a return to a seven-district Town Council and adding an eighth member to the Board of Education, in which the two parties have staked out opposite positions. And Kelly has his eyes on the up-ballot race.

“Trumbull has not gone for a Democratic presidential candidate since Lyndon Johnson beat Barry Goldwater in 1964,” he said. “They say you’ll never achieve a goal if you’re afraid to say it out loud, so let’s make this the year.”