In Boston, two LGBT groups - Boston Pride and OutVets - were allowed to participate for the first time and for the first time since homosexuals were prohibited by the U.S. Supreme Court to participate in the parade, a Boston mayor marched as well.

Boston Pride organizer Sylvain Bruni called the move "a tremendous leap forward,'' according to the Boston Globe, and Mayor Marty Walsh said, ''With this year's parade, Boston is putting years of controversy behind us."

The Knights of Columbus did not say outright that they refused to march because gay groups were admitted for the first time.

According to a statement on the Massachusetts State Council of the Knights of Columbus website: "The Massachusetts State Council of the Knights of Columbus had planned to march in the 2015 St. Patrick's Day Parade as a Catholic witness, to honor this great Catholic saint and in gratitude for the contributions of Irish Americans to the history of our country. We did so in the belief that the St. Patrick's Day Parade would be an occasion for unity and celebration in the city of Boston. We deeply regret that some have decided to use this occasion to further the narrow objectives of certain special interests, which has subjected this occasion to undeserved division and controversy. In addition, certain groups have chosen to misrepresent our reason for marching, insisting that we were participating in the parade to support another group or for political reasons. Such allegations are complete fabrications and have no basis in reality whatsoever. Because the parade has become politicized and divisive, and because of the misrepresentation of our motive for participating, we will not be marching in this year's parade. Instead we invite Catholics to join us in prayer to celebrate St. Patrick during the hours of the parade."

The Knights of Columbus weren't the only group to pull out of the festivities.

''We don't want to be seen as condoning homosexual activity and gay marriage,'' said Immaculate Heart of Mary School's principal, Brother Thomas Dalton, according to the Boston Globe. The school had participated in the parade for 25 years before its boycott on March 15.

But Bruni told the Boston Globe that the participation of Boston Pride wasn't intended as a political move. ''For us there is no political agenda," he said. "Our job is to ensure the visibility of our community, and our message is, be as respectful as you would be in our Boston Pride parade."