It is possible that a structure earlier than 1135 was on the site. Unlike Kenwyn and Kea Truro did not have a Celtic origin.
1135-1170 Possible period of the building of the church known as St Mary's although in "the parochial History of Cornwall " by Davies Gilbert suggests that it was dedicated to St Pancras.
1259-Bishop Bronescombe set out from Exeter on a prolonged tour of parts of his diocese on the 2nd of September this year. On the 28th of September he dedicated the chapel of St Mary, (whether at this dedication the name was changed to St Mary from St Pancras) which was to become the parish church that later would form the nucleus of the Victorian Cathedral in Truro.
1346-The badge of the Prince of Wales in a field three ostrich feathers with this motto "Ich Dien " I serve. was won at the battle of Crecy from John of Luxembourg, King of Bohemia by Edward the Black Prince the first Duke of Cornwall. It states in Hals Manuscript "which arms we may conclude were erected in a glass window soon after the victory, he being High Lord of this borough ".
1548-St Mary's was rebuilt, but not completed for the wont of funds.
1591-Church Registers commence from this year.
1641-John Robarts Died on the 21st day of March in his 70th year and was buried in St Mary's Church (His memorial made of Alabaster can still be found in the North aisle of Truro Cathedral ) son of Richard Robarts he married Phillippe daughter of John Gavrigan of Gavrigan of Cornwall by whom he had a son Richard Robarts Knight and later Sheriff of Cornwall. John Roberts was mayor of Truro and the member of the family to found the Lanhydrock Estate near Bodmin.
1714-The monument as stated thereon "was erected out of pious regard for teir memories" the memories of the Burgess Family. Anne Burges and Francies Burgess and his wife daughter and heiress of Richard Trenwith of St Erth. Humprey Burgess Buried April 27th 1679 of five survived Edward Humprey and Mary Burges the other seven died in their infancy buried 16th October 1684 31st August 1688 Judith daughter of said Francies and Anne Burges Nanwyden.
Note.-The Bishops of Devon and Cornwall, and their staffs, found it difficult task to administer to the needs of so large a territory, over the years the population increased, this made their task more arduous .Letters and articles were put forward by leading figures during the 19th century, both from the church and the laity, advocating the re-instatement of the Cornish bishopric without success. The visits to Cornwall of the bishop were infrequent and when he came he had much to do, particularly in conducting mass confirmations.
1824-August 4th -Between five and six hundred were received by the Bishop for confirmation.
August 5th-A further one hundred and forty were received.
1842-August 9th Bishop Philpotts confirmed 400 school-children, at that time, he was recovering from an accident and had to be conveyed to the church in a sedan chair.
1876-August 17th the act of Parliament was passed creating the Bishopric of Truro. The Order of the Council stated that St Mary's church should be a Cathedral and the first bishop was named as Dr E W Benson.
St Marys was demolished apart for a small south aisle that was incorporated in the new Cathedral possibly to maintain certain endowments. Some of the memorials as stated above were also transferred into the Cathedral.