Sir Philip Sydney Jones built "Llandilo House" in 1878 on a large property bounded by The Boulevarde, Albyn Road, Kingsland Road and Wakeford Road and lived there until his death in 1918. The property was then subdivided and a group of Strathfield residents headed by Rev Wheaton, a Congregational minister, bought the house for a school which was known as Strathfield Grammar School. In 1926 it was offered to Trinity Grammar School and bought by them but Strathfield Grammar School and Trinity Grammar School continued to function as separate establishments until 1932, when the two became Trinity Grammar School. From 1932 until 1937 all teaching (except some Science) was done at Strathfield and boys were taken by bus to Summer Hill for sport. (The boarders lived at Summer Hill). 1938 saw a division - the Senior School returning to Summer Hill and Strathfield being established as the Preparatory School.

"Lauriston", on the corner of The Boulevarde and Margaret Street was leased from the Vickery family in 1946 as a boarding house for Preparatory School boarders and was used during the day as the Sub Primary. It was purchased in 1951 but sold in 1967. "Milverton" had been bought from Dr. Hotton in 1966 and the Sub Primary moved there. Prep. boarders had moved to Summer Hill at the beginning of 1966. "Milverton", though separated from "Llandilo" by "Somerset" was accessible from "Llandillo" by a right of way at the rear of the "Somerset" property.

On the death of Lady Joske, whose first husband, James Larcombe, had built "Somerset" in 1932, the School was able to buy this property, giving much-needed additional space to the Preparatory School.

Over the years a considerable amount of extension and renovation has taken place on both the "Llandilo" and "Milverton"properties, the latest such renovations and magnificent extension at "Milverton" being opened in 1991. The whole Infants' Department is now located at "Milverton".

Though Trinity Grammar School now occupies a much larger area than that bought from Strathfield Grammar School, the total is much less than the original "Llandilo" site owned by Sir Philip Sydney Jones.