While New Hampshire is doing more than its share of bolstering the number of women on Capitol Hill, six states — Alaska, Delaware, Iowa, Mississippi, North Dakota and Vermont — have never elected a woman to the House. And four of those — Delaware, Iowa, Mississippi and Vermont — have never sent a woman to the Senate.

The state after New Hampshire, with the next highest proportion of women in its Congressional delegation, is Hawaii, where both House members and one senator are women.

In only three other states, Maine, Missouri and Washington, do women make up at least half of the delegations. Sixteen states, including New Jersey, have no women in Congress.

Although the women in New Hampshire are serving all at once by happenstance, women have long held prominent positions in New Hampshire government.

One reason is the size of the State House, a typical pipeline for aspiring politicians. It has 400 members, making it the largest of the states and the fourth-largest governing body in the English-speaking world (after the United States Congress, the British Parliament and the Indian Parliament). With so many seats available, women have a better chance of being elected in New Hampshire than they have in many other states.

New Hampshire also has a long history of volunteerism, and serving in the General Court, as the legislature is known, amounts to an act of volunteerism because it pays just $100 a year, plus mileage. Every year since 1975, more than 100 women have served.

“There are lots of opportunities for women to pitch in, prove their competence and learn a lot about governing and the political process,” Ms. Hassan said in an interview. “We’ve had a very deep bench of women.”