Her experience is increasingly the norm. While independents have long thrived here, the number of so-called unenrolled voters has downright surged in recent years, with a mix of bureaucratic and ideological currents working to swell the ranks of independents to 61 percent of the state’s 4.7 million voters.

That, by one analysis, is the highest share of unaffiliated voters in any state in the country, a surprising reality given Massachusetts’ deep blue reputation and history of Democratic dominance at the ballot box. The growth here also bucks the trend in other New England states, where both the Democratic and Republican parties have tightly guarded their share of the electorate, or even added to them at a time of intense political polarization nationwide.

“The Republican Party up to very recently was moving very far to the right and . . . the Democratic Party has been moving very far to the left,” Secretary of State William F. Galvin, an eight-term Democrat, said of the state parties, both of which have seen membership plunge.

Democrats, who once made up 45 percent of voters in 1990, now account for just 29 percent. Fewer than 9 percent of voters currently declare themselves members of the Republican Party.

Left in the middle, Galvin said, are those who agree with the parties on some issues, but don’t want to be affiliated with them. “It gives them no place to go — and no reason to,” he said.

Technically, nowhere is that middle lane bigger than in Massachusetts, and few appear even close to matching the number of independent voters here, either. Alaska is close, with about 58 percent of its registered voters not affiliated with a party, but no other state among the 30 that record party registration had independents break 50 percent of its electorate last year, according to data compiled by researchers for a study of voter registration patterns.

An array of factors likely contribute to Massachusetts’ bulbous independent bloc. Election rules vary widely by state, but here, unenrolled voters can participate in any partisan primary they choose. The state also has a relatively new law that automatically enrolls people to vote when they get a driver’s license or health insurance through the state, which has pushed hundreds of thousands of voters without party designation onto the rolls.

The major parties’ lurch toward the fringes also plays a role, experts say. Some voters think, “ ‘If I don’t check all the boxes, then I can’t be a Democrat,’ ” said Shanique Spalding, executive director of Massachusetts Voter Table, an advocacy group.

How much the move away from party affiliation has impacted actual election results is debatable. Democrats have long dominated elected office in Massachusetts, holding every one of the state’s seats in the House of Representatives since the mid-1990s. Massachusetts has sent just one Republican to the Senate — Scott Brown — in the last 45 years.

Outside of the Legislature — where the GOP is the super-minority — Republicans hold just one of the state’s 11 district attorney seats, and just two of the 14 sheriff’s offices.

“Independents do have a party preference. They just tend to not want to make that known,” said Enrijeta Shino, a University of Alabama assistant professor of American politics and coauthor of the study examining voter registration trends, specifically in Florida and North Carolina. Independents tend to be younger, more moderate, and less politically active voters, she said, but some also are simply “closet partisans.”

“If a state has more registered independents, those people still [likely] have to vote for one of the two main parties’ candidates,” she said.

The electorate’s makeup here could, however, help explain one of Massachusetts’ more peculiar voting habits. Moderate Republicans from Bill Weld to Mitt Romney and, most recently, Charlie Baker, dominated the governor’s office for the better part of three decades even as progressives such as Senator Elizabeth Warren and Representative Ayanna Pressley handily won their races at the federal level.

“We are open to Republican managers and Democratic activists for Congress,” said David Paleologos, director of the Suffolk University Political Research Center, which has done polling for the Globe. “Underneath that umbrella of 60 percent, there’s a method to the madness.”

That so many voters also choose to identify as independents may be exacerbated by something else in Massachusetts, experts say: With little competition in both primaries and general elections cycle after cycle, voters are often given little reason to join a party’s ranks.

The website Ballotpedia, which tracks elections nationwide, last year rated the state’s legislative elections as the least competitive in the country, based on factors including how often an incumbent faces a challenger. The state ranked last in 2020, 2018, and 2016 as well. Congressional incumbents in Massachusetts have lost a seat just twice in the last 27 years, both times in the Democratic primary. A sitting governor hasn’t lost in four decades.

“Incumbents win over and over again, people are not running for office, and we have all these elections where there’s basically nothing really happening,” said Rachael Cobb, chair of the political science and legal studies department at Suffolk University. “That is not the recipe to increase party participation.”

To be sure, the share of unenrolled voters has been steadily climbing in other states, data show, and the growing independent bloc in Massachusetts is not an entirely new phenomenon. After decades of Democratic dominance, unenrolled voters outnumbered Democrats by the end of 1990. They haven’t dipped below 50 percent of the electorate since 2008.

But their numbers have ballooned of late. In the last three years alone, the state has added more than 356,000 unenrolled voters, more than doubling the rate of growth from the previous three-year stretch.

Rules, as much as politics itself, matter. Massachusetts is one of just nine states that open their primaries to unaffiliated voters, giving a big incentive to residents to not enroll in a major party while still having a chance to decide its nominee. (In 15 other “open primary” states, anyone can vote in the nominating race.)

The adoption of automatic voter registration five years ago also appears to have helped juice the state’s numbers. Under the law, roughly 554,000 people have been registered to vote since 2020, all as independents, according to state data.

It’s possible some may have later chosen to join a party. But the growth of independents has far outpaced the overall increase in the electorate, with even more voters likely to flow onto the rolls in the coming years. The Legislature last year passed new language removing the option residents once had to opt out of automatic voter registration.

Elsewhere in New England, the electorate has shifted the other way. While most other states are seeing some gains in independent voters, in New Hampshire, very little has changed in recent years, despite the state’s semi-open primaries: Democrats and Republicans each make up nearly 31 percent of registered voters.

The share of Republicans in Rhode Island — where, as in Massachusetts, Democrats dominate elected office — has actually increased slightly since 2016, according to data compiled by the Globe. And in Maine, where a new law recently took effect to open state and presidential primaries to independents, Democratic registration in particular has surged, pushing the party’s share of voters to 37 percent last year.

That could change slightly with the new law, as people no longer have to be party-affiliated to pull a primary ballot, said Mark Brewer, a political science professor at the University of Maine. But the rise in partisanship is evidence of the slow death of moderate politicians, he said, even in Maine, which boasts one of just two Independents in the Senate in Angus King (Bernie Sanders of Vermont is the other) and a centrist Republican in Susan Collins.

“The reality,” he said, “is most independents lean” toward one party or the other.

Mason Ashcraft, 42, of Westborough, said he’s been an unenrolled voter since moving to Massachusetts permanently in 2010, and has always been “wary of hyper-partisanship.”

But he said he’s also always pulled a Democratic ballot when given a choice. His “sympathies,” he said, lean left, especially now.

“As things are,” he said, “I just can’t abide the thought of voting for anyone on a Republican ballot.”

Matt Stout can be reached at matt.stout@globe.com. Follow him @mattpstout.