John McElroy was born in Brookeborough, County Fermanagh and emigrated to America in 1802. He entered the Society of Jesus as a lay brother and was ordained in 1817. He built a church, a college, schools and an orphanage in Frederick, Maryland. He served as army chaplain during the Mexican War, and from 1847 to 1862 he was in Boston, where he built a church and a college. He died in Frederick, Maryland.