The parish came into being sometime from 1536 on but the first clerical records related to it are later. One, the calendar of Bishops of Waterford, notes that Marmaduke Middleton, Vicar of Coolock, was consecrated as Bishop in 1579. The second, from 1615, refers to one John Credlan as "Rector of Coolock and Curate at Rathenny". It is believed that the predecessor of the older St. Assam's Church in Raheny was built in the same period, c. 1609. By 1641, the Vicar of Coolock was Thomas Seele, who was also during his career Dean of St. Patrick's Cathedral and Precentor of Christ Church Cathedral.
New church
In 1760, a Parish Church, the Church of St. John the Evangelist was built on the site of the ruined Church of St. Brendan, on the banks of the Santry River at Tonlegee Road, opposite the Holy Well of St. Brendan, and later, a parochial hall was added. In 1820, the rector was Henry Moore, and from no later than 1837 to the 1860s, the office was held by William Maconchy, who is recorded as marrying Anna King at the parish church in 1823. In Samuel Lewis's Topographical Dictionary of Ireland, the summation for 1837 is:
The living is a vicarage, in the diocese of Dublin, and in the patronage of the Marquess of Drogheda, in whom the rectory is impropriate: the vicarial tithes amount to £249. 4. 7½. There is a glebe-house, with a glebe comprising 17a. 2r. 25p. The church, dedicated to St. Brandon, a neat edifice, was partly rebuilt and enlarged, by aid of a loan of £500 from the late Board of First Fruits, in 1818.... The parochial school, for which a house was built at an expense of £300, the gift of Sir Compton Domville, Bart., is supported by subscription, and, attended by 30 or 40 children. A school of 30 children, for which a handsome cottage has been built in the grounds of Beaumont, and an infants' school in connection with it, are wholly supported by Mrs. Guinness...
The Lewis article includes the interesting points re. the right of presentation for the parish, the substantial glebe and tithe, and raises a question about the name of the church.
Towards Union
The Parishes of Raheny and Coolock shared in outings, Sunday School activities, the parish magazine and the World War I memorial in the years prior to 1920, and the Union of the parishes was first proposed in 1920. In the event, Coolock was instead placed in Union with the Parishes of Glasnevin and Santry. The Holy Well was covered over in the 1950s. Coolock was eventually placed in Union with Raheny in 1960. The Rector of Raheny was appointed in charge of both in March 1960, and the union was completed when he became Rector of Coolock in July of that year. From then on, there was to be a rector in Raheny, a curate in Coolock, two churches, and a shared school. For over twenty years, the Select Vestries of the parishes were also united, but this ended in 1981. The next rector of the United Parishes was Wilbert Kelly, appointed in 1970, and he was succeeded in 1975 by Cecil Wilson, then by James "Jim" Carroll, and in 2013 by Norman MacCausland. The united parish also holds the Church of Ireland chaplaincies of Beaumont Hospital, St. Joseph's Hospital and St. Francis Hospice.
