Is Vermont the Most Populous New England State?

No—Massachusetts Is

Per the 2020 U.S. Census:

• Massachusetts: ~6.89 million
• Connecticut: ~3.61 million
• New Hampshire: ~1.38 million
• Rhode Island: ~1.09 million
• Maine: ~1.36 million
• Vermont: ~643,000 (least populous)

Vermont is the second-smallest by population (ahead of only Wyoming nationally).