On this St. Patrick’s Day, Members of Congress who care about Ireland have a lot to celebrate.

The final piece of the Good Friday Agreement passed the Northern Ireland Assembly last week, in many ways closing a chapter in the tumultuous history of relations between Ireland and Northern Ireland. And that came with a great deal of help from their American peers. Since the 1970s two bipartisan groups of Congressmen have been working to foster peace on the Emerald Isle, and they feel good about how far it has come.

Irish issues are important to the U.S. less for military or economic reasons than for personal reasons. The Census Bureau says 36.3 million Americans claimed Irish ancestry in 2008, making it the second most frequently reported ancestry (German is first) and making the Irish-American population more than eight times the population of Ireland itself. Some Members most involved in the issue are of Irish ancestry themselves, while others represent districts with large Irish populations.

Former Rep. Jim Walsh (R-N.Y.) was in Belfast for the vote. The grandson of Irish immigrants, Walsh led the Congressional Friends of Ireland group from 1995 until he left Congress in 2008.

The vote “for me personally was the most significant thing,” Walsh responded when asked about his proudest achievement in working with Irish officials.

As they have been at every stage of the peace process, Members of Congress were involved in this vote. Its passage would transfer policing authority in Northern Ireland (still a part of the United Kingdom) from London to Belfast. As the vote neared, Ulster Unionist legislators who generally prefer reliance on the United Kingdom declared their opposition to the bill. A number of American politicians made calls in support of the bill, including Secretary of State Hillary Rodham Clinton and former President George W. Bush. Four representatives of both the Friends of Ireland and the Ad Hoc Committee on Irish Affairs, the two Congressional groups, released a stern statement.

“On Tuesday, the eyes of the world will be on Belfast and the Ulster Unionist party,” they wrote. “The choice they make will have significant and lasting consequences. They can vote yes for a more peaceful and prosperous future. Or they can be on the wrong side of history and vote for the past.”

The vote ultimately passed 88-17 and will take effect April 12.

This was only the most recent example of American lawmakers urging their Irish counterparts toward peace. In 1977, then-Rep. Mario Biaggi (D-N.Y.) founded the Ad Hoc Congressional Committee for Irish Affairs as a way to engage Irish-Americans in the peace process. Soon after, the Friends of Ireland — led by the “four horsemen,” Speaker Tip O’Neill (D-Mass.), Sens. Daniel Patrick Moynihan (D-N.Y.) and Edward Kennedy (D-Mass.), and New York Gov. Hugh Carey (D) — was formed. Initially the Ad Hoc Committee was seen as more radical and the Friends of Ireland as more moderate, but over the past 15 years the two groups have worked together almost seamlessly, according to Rep. Richard Neal (D-Mass.), the current leader of the Friends of Ireland and a former leader of the Ad Hoc Committee.

“I think our game plan really was to try to consolidate the two,” Neal said.

The Speaker traditionally appoints the leader of the Friends of Ireland, while leaders of the Ad Hoc Committee are two Republicans and two Democrats. Members of the groups convene whenever an Irish official comes to Washington, D.C. That means they meet about once a month, and nowadays they focus more on longer-term economic and immigration issues than the more urgent issues that they discussed in the past.

“We used to have a crisis every week or two at one time,” said Rep. Peter King (R-N.Y.), who became a co-chairman of the Ad Hoc Committee in 1995.

At times when Irish politicians of opposing parties would not occupy the same space on their side of the Atlantic Ocean, they would get together and talk on neutral ground in the U.S., Walsh said. In his first-ever trip to the Emerald Isle in 1995, leaders of one party would wait to meet with them until leaders from another party had left the building. Over time, after President Bill Clinton granted Sinn Fein leader Gerry Adams a visa to the U.S. in 1994 and the Good Friday Agreement was signed in 1998, that changed.

Each step in the process meant new revelations for everyone involved. Rep. Joe Crowley (D-N.Y.), now a co-chairman of the Ad Hoc Committee, remembered an epiphany that he had at an economic forum in 1995 when he was still a state legislator. It was the first time he met politicians from Northern Ireland.

“For me it was the beginning of the understanding that one could be Irish yet British,” he said, in the same way that “I’m American but feel Irish as well.”

For those Members who feel like Crowley, St. Patrick’s Day continues to be a highlight — and the festivities last throughout the week. Members covet invitations to the Speaker’s St. Patrick’s Day lunch, where the Friends of Ireland chairman sits at a head table with Irish leaders, the Speaker and the president. In the evening, the president invites a similar group to the White House for dinner. This year the American Ireland Fund held a dinner Tuesday night, a briefing is planned on the Hill on Thursday morning and another reception will honor murdered civil rights lawyer Pat Finucane Thursday night.

On a day set aside for the patron saint of Ireland, American legislators will enjoy a Guinness or two and maybe even toast the contributions that they’ve made to peace in Ireland.