Approximately one in three residents of the US and nearly half of all American Christians are Catholic making it the most populous denomination in the US. The next largest denomination, the Southern Baptists, has only one fourth as many members.
Thank you for making my point!
The vast majority of Americans (67%) are not Catholic.
Catholics may makeup a majority of Christians, and be the most populous denomination of Christians, as you state, but they are not the majority of Americans, as I stipulate.