"Not really. The Catholic sect of Christianity is the largest in America by a fair amount."
I believe that about 22% of Americans are Catholic, but over 65% of Americans are Protestant. The numbers vary, depending on where you look, but they move around those axes. There are between two and three times as many Protestants as Catholics in the US.
Now, it is true that the largest single denomination is Catholicism, but that is because the various forms of Protestantism are divides into smaller sects. If you add together the various Evangelical sects and you've got a huge number of people.
It's improper to refer to the Catholic Church as a "sect of Christianity".
Actually Catholicsm is growing as a share of American Christianity. About 24% now. But that misses the point. Catholics are NOT a distinct minority. Atheists and Buddhists yes, but not Catholics and conservaitve Catholics, conservative Protestants and conservative Jews are aligned in the culture war.