John McElroy SJ (14 May 1782 – 12 September 1877) was a Jesuit priest who founded Catholic schools in the United States.

After emigrating to the United States in 1803, McElroy enrolled in Georgetown University in 1806, the same year in which he joined the Society of Jesus as a lay brother.

In the hopes of providing a better life for John and his brother Anthony, their father, a farmer, financed their travel to the United States of America.

In 1803 the two young men boarded a ship leaving the port of Londonderry and arriving in Baltimore, Maryland, on 26 August.

[5] McElroy managed the school's finances so well that through the period of economic hardship following the War of 1812, he was able to send several Jesuits to Rome to study.

[7] In 1819, McElroy started a Sunday School for black children who were taught prayers and catechism simultaneously with spelling and reading, by volunteer members of the congregation.

In 1823 he began negotiations with the Sisters of Charity in Emmitsburg, Maryland, for the establishment of a school for girls in Frederick.

In 1824, the St. John's Benevolent Female Free School was founded by the Sisters of Charity of Saint Joseph at 200 East Second Street in Frederick.

[12] Shortly after the Mexican-American War began in 1846, many Irish Catholic immigrants joined the U.S. forces in Mexico.

In a discussion between the President of the United States of America, James K. Polk, and Archbishop John Hughes of New York, it was decided that for the first time, Roman Catholic priests would join US Army forces as chaplains.

Two important gifts were received, a bequest of $3000 from Joseph Coolidge Shaw, and $5000 plus all construction expenses from Catholic philanthropist Andrew Carney.

[8] In 1858, Bishop Fitzpatrick and Father McElroy broke ground for Boston College, and for the Church of the Immaculate Conception.

His eyesight was failing and while moving through his home he fell, fracturing his femur, which would eventually lead to his death[22] at the Jesuit novitiate in Frederick.