Directly behind the original church site at Royal Orchard Boulevard and Yonge Street is the historic and still active cemetery of Holy Trinity Church, Thornhill, which contains graves dating from 1832 when cholera took many lives. There is a small number of interments each year. There is also a Memorial Garden for cremated remains. Annual maintenance is performed by specialists to raise sunken tombstones and repair broken ones. Despite its proximity to busy Yonge Street, the cemetery remains a peaceful and beautiful resting place.
Although separated from the church buildings, the parish maintains the cemetery through an active Cemetery Committee. The Committee manages the sale of the few remaining burial plots, direct internments and maintains the records as required by provincial law. Answering queries about ancestors is also handled by this team. They contract for restoration of monuments as required and clean up the site regularly.