St Eunan's College ( ; ), known locally as The College to distinguish it from the cathedral and GAA club, is a voluntary Roman Catholic all-male, English-medium secondary day school (and former boarding school) in County Donegal, Ireland. It is located upon Sentry Hill in Letterkenny. Named after Adomnán or Eunan (the Abbot of Iona who was native to Tír Chonaill, mainly modern County Donegal, and is patron saint of the Roman Catholic Diocese of Raphoe), the school's foundation stone was laid on the patron saint's feast day of 23 September.

Its buildings and grounds include the College Chapel, a medial courtyard and playing fields. Architectural features include four turreted round towers and flying buttresses which are modelled on the nearby Cathedral. Sporadic extensions have occurred, including during the early 1930s and the late 1970s – science laboratories and a demonstration room were added in between these two periods of major building work. A monkey puzzle tree grows on the front lawn close to the front door and the College Chapel. Those men who have attended the college are termed Old Adomnánians ().

Sportsmen educated there include Olympic athletes, Mark English (a middle-distance runner) and Philip Deignan (a cyclist who later turned professional), as well as several current county footballers, among whom are Michael Murphy, Shaun Patton and Niall O'Donnell. Several members of Cabinet were educated here, including Pa O'Donnell, Neil Blaney and Jim McDaid. Others educated there include quiz player Pat Gibson (Who Wants to Be a Millionaire?, Mastermind, Brain of Britain, Mastermind Champion of Champions, Eggheads), actor Ray McAnally and lexicographer Niall Ó Dónaill.

The college has a tradition since its foundation of hosting musicals, operas, operettas and other performances. Its current principal is Damien McCroary. The All-Ireland-winning Gaelic footballer, Colm McFadden, serves as his deputy. Other staff members (past and present) include Ollie Horgan, Gary McDaid, Charlie McGeever, Caolan McGonagle, Caolan Ward and John Wilson, who later served as Tánaiste. It accommodates close to 1,000 students and increases its numbers year-on-year.

History Antecedent institutions: 1700s–1800s Anthony Coyle, the first Bishop of Raphoe to take up residence in Letterkenny, established a classical academy during the eighteenth century. Then, in the following century, Bishop Patrick McGettigan appointed a priest as a teacher of Greek, Latin and mathematics at a building on Castle Street in 1825. The school was abandoned by the mid-1830s due to a priest shortage and a professor having died. A further school followed during the 1830s, close to the current college, though it too was short-lived, as was another school in the town during the 1840s.

In 1849, Bishop McGettigan approved the setting up of a school in the Literary Institute; this would become known as the "Old Seminary" and the "Latin School". This was the final school before the college was established and the longest lasting of its antecedents. Run independently for three decades, in 1879 the Bishop formally placed it under the management of the Catholic Church after the last of various doctors and other men, who had until then run the school, died prematurely. The recently ordained Edward Maguire, then aged 24, was appointed president. Maguire had, by the 1880s, been sent to Maynooth. Patrick McCaffery succeeded him as president; he, in his turn, was succeeded by P. J. Brennan in 1889. J. J. O'Doherty succeeded Brennan as president; O'Doherty then gave way to the last president of the Old Seminary, Hugh Gallagher.

As scholar numbers began to outgrow the facilities available at the Literary Institute, Bishop of Raphoe Patrick O'Donnell sought to establish a boarding school to provide a classical education. The college was established as a minor seminary to prepare young men for the priesthood of the Catholic Church. Diocesan colleges experienced an increasingly favoured stature at the time and were set up to give an unrivalled Catholic education to boys of every class. The college's motto, In hoc signo vinces, meaning "by this sign – (the Cross) – you shall conquer" is derived from the episcopal motto of O'Donnell.

Foundation, fire and the national grid: 1904–1944 In 1904, the college's foundation stone was laid on the feast of St Eunan (23 September). Priests from the Roman Catholic Diocese of Raphoe gathered money from around the world for its erection. The college opened in September 1906, with Edward Maguire as its first president. Latin, Greek and history were taught. Maguire remained as president of the college until 1910 when he was sent to another parish.

Michael Ward succeeded Maguire as president; he had been at the college since its opening four years previously and served as president until his sudden death aged 41 in 1919. During The Rev Ward's Presidency, a student died in 1912 and there was a fire in the college.

Patrick D. McCaul became the third president of the college; he too had taught there since its opening but had been appointed to the cathedral parish in 1918, only to be brought back after Ward's death. McCaul's tenure, which lasted until he was sent to another parish in 1929, coincided with increased student registrations and made an extension to the college much needed. This was built in the early 1930s during the tenure of John Kerr, the only president of the college to succeed to the presidency without having been a member of the teaching staff — until, that is, the arrival of Christopher Darby from Ballyshannon's Coláiste Cholmcille in 2009. Kerr's tenure lasted until 1944, at which time he was sent to another part of the county. Kerr's presidency included the college's Silver Jubilee in 1931 and, like Ward before him and others later (Carney, McCroary), coincided with the death of a student; in this case he was brought to the district hospital in pain in October 1933, but died on 7 October. The same year (1933), the college was connected to the ESB national grid for the first time. Until that time, it had obtained electricity from a system McCaul had near the college's handball alleys.

Chapel, opera, telescope and playing field: 1944–1971 Arthur McLoone was the college's fifth president and the first to have studied at the college (beginning in 1911). A classical scholar, he taught Latin and Greek, served as dean and as bursar and involved himself in the college's annual opera; he had a special fondness for the operettas of Gilbert and Sullivan. His ten-year presidency of the college is noted for the development of the first playing field opposite the college and the new College Chapel which was finished in 1952. He was noted for his administrative ability. Sent away to Killybegs in mid-1954,. McLoone's death came all of a sudden during celebrations for the college's Golden Jubilee in 1956.

Christopher Finnegan, sixth president of the college, was with its founder Cardinal O'Donnell on his death in 1927. He taught English, had been vice president of the college since 1944 and worked with McLoone in the staging of his beloved Gilbert and Sullivan operettas. A gifted preacher and eloquent orator, he oversaw the building of the Recreation Hall in 1958, before dying in office aged 61 in December 1960.

Daniel J. Cunnea (known as "The Doc"), seventh president of the college, was also educated there. After completing a doctorate and spending some time working at Knockbeg College, he joined the St Eunan's staff in 1942 as a teacher of science and mathematics. With Finnegan having just suddenly died, e Cunnea was propelled into the presidency in January 1961. Noted for his use of a telescope to study the night sky, he oversaw improvements in the college's science facilities, including two science laboratories and a demonstration room in 1964, before being sent to a remote village in another part of the county in 1969.

Peter McMahon, eighth president of the college, had, like his predecessor, been educated there and joined the staff in 1953, holding the posts of Dean and Bursar (just as McLoone had before him). McMahon was president for two years, bridging the gap between the 1960s and 1970s. Though sent to administer a nearby rural parish, he remained as a member of staff and taught mathematics at the college until 1981.

"Free education" and demise of boarding: 1971–present Austin Laverty, ninth president of the college, had also studied there and, like McLoone and McMahon, held the posts of Dean and Bursar. Appointed to the presidency in 1971, he steered the college through the difficult years that followed the introduction of "free education" by Donogh O'Malley, who made the decision without consulting his colleagues in cabinet. With a growing population of children to be accommodated, the curriculum overhauled, and classical subjects demoted to suit the needs of the less able, the less academic child introduced to the realities of an advanced secondary education, an extension to the college was required by the mid-1970s. Work got underway in 1977, ended in 1979, and the "New Building" was inaugurated in 1981, the 75th anniversary of the college's foundation. Laverty began improvements to the college's boarding facilities but departed in January 1982 to become cathedral parish administrator.

Daniel Carr, tenth president of the college, studied there too and joined the staff. During nearly seven years as president, Carr continued improvements begun under his predecessor and encouraged the college's first computer network of BBCs (a first for the county). The first computer in the school was an Apple II. Edward Harvey was the teacher who began a computer club at the college in 1980. With the number of boarders declining under Carr's presidency, some dormitories could be turned into classrooms. In 1988, Carr was sent to the same remote village in another part of the county as Cunnea (who had retired), though Carr recovered to receive the title of monsignor.

Cathal O'Fearrai, eleventh president of the college, had been recalled from Dublin in 1982 by Bishop of Raphoe Séamus Hegarty and posted to the college's teaching staff. Six years later he became president, overseeing the creation of a computer laboratory, an all-weather pitch, and a front playing field. With the development of secondary schools in the county, the number of boarders at the college continued to decline and in 1992 the college's boarding wing was shut. This allowed the president to create a library and more classrooms from the last available boarding facilities, an achievement completed before he was sent away in 1996.

Michael Carney, twelfth president of the college, like many of his predecessors studied there. He was the college's organist and assistant director of the college's choir (1980–83) before being appointed to the college's teaching staff in 1989–90, teaching history, music, and religion, until assuming the presidency in 1996. As president, Carney accompanied students and teachers of the German language to Vienna, Austria in 1999. Links with other continental schools were also developed, including a school in Perros-Guirec, Brittany in northwestern France. The annual ski trip began in 1997. Other events during Carney's presidency included the separate deaths of, first, a student and, later, a member of the teaching staff — Antoin Ó Colla of Cloughaneely, who had taught Irish, history, and geography at the college since 1974 (the same year he graduated from University College Galway). In addition, the college celebrated its centenary year in 2006. Carney served as president of the college until 2009, taking up residency as priest at Ramelton where he was in situ when local scientist William Cecil Campbell won the 2015 Nobel Prize in Physiology or Medicine.