According to George Phillies in IPR comments
NH Representative Joseph Stallcop (Cheshire-4) announces joining the Libertarian Party of New Hampshire and NH House Libertarian Caucus with Rep. Caleb Q. Dyer
Stallcop, who is a college student, was elected as a Democrat. The Atlantic mentioned him last year in an article about young Bernie Sanders supporters. Last month he joined several other people in smoking marijuana on the grounds of the State House on 4/20. Here is a newspaper profile from when he took office.