Peter O’Neill was born at Loup, County Londonderry. He lived with his wife, Esther, at Ballygillen, Ballinderry Bridge, Coagh. Peter and Esther had a son, Joseph James O'Neill, who was born about 1911. He enlisted in Cookstown with 1st Battalion Royal Inniskilling Fusiliers and was posted to Gallipoli. He was killed in action, on 30th May 1915, while his battalion was in Brigade reserve at White House, Gallipoli.

Take the road opposite the Kabatepe Museum to Helles/Alcitepe. After 14.2 km's, take a right turn at the 'T' junction to Twelve Tree Copse and other Helles cemeteries. After 14.3 km's take the left fork and the cemetery will be found on the right after 15.4 km's. Twelve Tree Copse Cemetery is in the Helles area, about 1 km south-west of the village of Krithia.