The first trace of Father John Larkin in the St. Dennis register was recorded in February of 1857. Of the twelve entries in the book made by Father Larkin four were for events at Athens (Lemont), three at Sag, one at Cass and four at Saint Dennis. Bishop Anthony O'Regan had requested Father Larkin to come to the Chicago Diocese to assist in the growing See. The bishop apparently had large plans for Father Larkin.

In late 1857 he assumed the pastorate of St. Mary's Cathedral in Chicago. By the close of the 1850's he was dispatched to St. Michael's Church in Galena following the work of Father Patrick McElhearne. Father Larkin was at St. Michael's Church in General Grant's hometown as the Civil War broke out.

Born in Deerpark, County Galway, John Larkin studied in the seminary at Maynooth College. Upon graduation John came to the United States in 1848 as the Irish holocaust was destroying the fiber of life there. Ordained in Baltimore on the 25 of October, 1849, Father Larkin spent some years in the Diocese of Pittsburgh as a missionary in the Allegheny Mountains before heading to Chicago. From 1849 until 1854 Father Larkin served at St. Mary parish in Freeport, Pennsylvania. From 1854 to 1855 he was assigned to St. Peter parish in Brownsville, Pennsylvania

Father Larkin, having been pastor at some of the major churches in Illinois at the time, decided to conquer New York City. Transferring to the Diocese of New York in 1861, Father Larkin spent time as assistant at St. Stephen's Church at 28th between Lexington and 3rd Avenue, "the largest and one of the most prestigious parishes in the city". Twenty years later St. Stephen's would become the center of conflict between the liberal movement of Reverend Doctor Edward McGlynn and the conservative response of Archbishop Michael Corrigan. It was a hotbed of ideas concerning the social reform movement that stood in opposition to political and "ecclesiastical machine" politics. Its effects are still felt today. Afterwards, Father Larkin moved to St. Michael's in Manhattan

In 1866, Father Larkin became pastor of the Church of the Holy Innocents near Broadway. The first Church of the Holy Innocents was a small frame building, originally an Anglican chapel under the same title. When in 1865 Father John Larkin was given the task of creating a parish in the semi-rural neighborhood of Broadway and West Thirty-seventh Street, he purchased the church property as a temporary shelter for his flock while he planned a beautiful Gothic edifice on adjoining lots. When his new Church of the Holy Innocents was nearly completed Father Larkin engaged the services of the distinguished Italian artist Francesco Brumidi to do an oil fresco of the Crucifixion above the main altar, similar to the one he had done in St. Stephen's Church just before Father Larkin left that parish. The new church was dedicated in 1870. [The Sisters of Charity of New York; 1809-1958, Volume II, Fordham University Press, New York, pgs. 46-7.] Father Larkin had the distinction of having had the first church in the New York Diocese (and possibly the world)"...to use electric light for church illumination at a time when the authorities hesitated, expecting a rebuke and prohibition from the Congregation of Rites for the innovation." [The Catholic Church in New York. John Talbot Smith. NewYork.1905.p.304] In 1872 he built the first school there. Father Larkin came to be known as an 'administrator of high rank' in the New York Diocese.

Being near to Broadway he had occasion to attend a play by Dion Boucicault entitled "The Shaughraun" at the Park Theatre. Boucicault had become accomplished in the Dublin theatre prior to immigrating to New York in 1853. From that time until 1890 he was a prime mover as a performer and playwright on Broadway. The play was reputed to be highly critical of the character of the Irish in relation to a scene about wakes. Father Larkin, without hesitation, lambasted the play from the pulpit the following day. His devotion to his native land would remain a hallmark of his character long after his passing. To this end the following is of interest: "At the time the English were celebrating the jubilee of Queen Victoria's reign, he [Father Larkin] announced a solemn requiem Mass for the anniversary of her coronation, in behalf of the millions of Irish done to death by English misgovernment. The ceremony was telegraphed around the world, and the incident became celebrated." [The Catholic Church in New York; p.304]

After serving the Church of the Holy Innocents for 24 years Father Larkin succumbed to pneumonia on the 20th of December 1890 at 70 years of age. A keen wit and a man with a purpose, Father John Larkin carried that spirit for many miles before finding rest in New York City.