In 1848 The Mercy Sisters founded their convent school (St. Peter’s Convent) in Pump Street in Derry to generate income to finance their ministry to the poor. Over time, their school numbers increased, necessitating a transfer from the grounds of the convent proper to new premises at Artillery Street (within the Walls of Derry), where the High School (Ard Scoil na Maighdine Mhuire – Convent of Our Lady of Mercy School) was established in 1887. 

In turn, the growing number of students attending the High School on Artillery Street required a further expansion of the school premises. With the closure of Watt’s Distillery and the estate at Thornhill on the outskirts of Derry, the Sisters of Mercy along with the kind assistance of Robert Boyle (a builder in Derry) purchased the Thornhill Estate in 1929. They adapted the house to meet the needs of the nuns and their boarders and in 1932, Thornhill College Convent of Mercy opened on the Culmore Road, along the beautiful banks of the Foyle.  
 

Thornhill College became established as the Catholic grammar school for girls in the Derry area in 1949. As the school’s roll continued to grow over the years peaking at over 1,500 students our present building and impressive facilities were established opening its doors in 2003, just across the Culmore Road from its former site. At this time the Sisters of Mercy withdrew from trusteeship of the school, passing it over to the Bishop and Diocese of Derry.