John F. Kennedy was a Catholic.
Kennedy attended Trinity Church (a Catholic church) while he was President.
From: Peter Roberts, "John Fitzgerald Kennedy" page in "God and Country" section of "Science Resources on the Net" website (http://www.geocities.com/peterroberts.geo/Relig-Politics/JFK.html; viewed 29 November 2005):
Religious Affiliation: Roman Catholic
Views on Religion and Politics:
JFK, being Roman Catholic, was acutely aware of the dangers of mixing religious and political institutions, and so was a strong proponent of the separation of church and state.
"It is my firm belief that there should be separation of church and state as we understand it in the United States -- that is, that both church and state should be free to operate, without interference from each other in their respective areas of jurisdiction. We live in a liberal, democratic society which embraces wide varieties of belief and disbelief. There is no doubt in my mind that the pluralism which has developed under our Constitution, providing as it does a framework within which diverse opinions can exist side by side and by their interaction enrich the whole, is the most ideal system yet devised by man. I cannot conceive of a set of circumstances which would lead me to a different conclusion." -- letter to Glenn L. Archer, 23 February 1959
"Whatever one's religion in his private life may be, for the officeholder, nothing takes precedence over his oath to uphold the Constitution and all its parts -- including the First Amendment and the strict separation of church and state." -- Interview, Look, 3 March 1959
"I believe the American people are more concerned with a man's views and abilities than with the church to which he belongs. I believe the founding fathers meant it when they provided in Article VI of the Constitution that there should be no religious test for public office. And I believe that the American people mean to adhere to those principles today." -- address to the American Society of Newspaper Editors, 21 April 1960
"I believe in an America where the separation of church and state is absolute--where no Catholic prelate would tell the President (should he be Catholic) how to act, and no Protestant minister would tell his parishioners for whom to vote--where no church or church school is granted any public funds or political preference--and where no man is denied public office merely because his religion differs from the President who might appoint him or the people who might elect him.
"I believe in an America that is officially neither Catholic, Protestant nor Jewish--where no public official either requests or accepts instructions on public policy from the Pope, the National Council of Churches or any other ecclesiastical source--where no religious body seeks to impose its will directly or indirectly upon the general populace or the public acts of its officials--and where religious liberty is so indivisible that an act against one church is treated as an act against all.
"For while this year it may be a Catholic against whom the finger of suspicion is pointed, in other years it has been, and may someday be again, a Jew--or a Quaker--or a Unitarian--or a Baptist. It was Virginia's harassment of Baptist preachers, for example, that helped lead to Jefferson's statute of religious freedom. Today I may be the victim--but tomorrow it may be you--until the whole fabric of our harmonious society is ripped at a time of great national peril.
"Finally, I believe in an America where religious intolerance will someday end--where all men and all churches are treated as equal--where every man has the same right to attend or not attend the church of his choice--where there is no Catholic vote, no anti-Catholic vote, no bloc voting of any kind--and where Catholics, Protestants and Jews, at both the lay and pastoral level, will refrain from those attitudes of disdain and division which have so often marred their works in the past, and promote instead the American ideal of brotherhood.
"That is the kind of America in which I believe. And it represents the kind of Presidency in which I believe--a great office that must neither be humbled by making it the instrument of any one religious group nor tarnished by arbitrarily withholding its occupancy from the members of any one religious group. I believe in a President whose religious views are his own private affair, neither imposed by him upon the nation or imposed by the nation upon him as a condition to holding that office.
"I would not look with favor upon a President working to subvert the first amendment's guarantees of religious liberty. Nor would our system of checks and balances permit him to do so--and neither do I look with favor upon those who would work to subvert Article VI of the Constitution by requiring a religious test--even by indirection--for it. If they disagree with that safeguard they should be out openly working to repeal it." -- address to the Ministerial Association of Greater Houston, 12 September 1960
"If my church attempted to influence me in a way which was improper or which affected adversely my responsibilities as a public servant sworn to uphold the Constitution, then I would reply to them that this was an improper action on their part. It was one to which I could not subscribe." -- press conference, Houston, Texas, 12 September 1960
"We do not want an official state church. If ninety-nine percent of the population were Catholics, I would still be opposed to it. I do not want civil power combined with religious power. I want to make it clear that I am committed as a matter of deep personal conviction to separation." -- interview, CBS-TV, Face the Nation, 30 October 1960