Designed in 1924 for Russell and Mabel Grimwade by Harold Desbrowe Annear, Westerfield is the most intact example of the series of houses Annear remodelled, or designed on the Mornington Peninsula in the 1920s which demonstrate the vitality of early twentieth century eclecticism. Moving away from the more formal urban Georgian style, Annear responds to the "playground" ambience of the peninsula with a range of formal attitudes. Westerfield itself is a Y plan half timbered house built on a granite base somewhat reminiscent of French country architecture.
However, the significance of Westerfield lies not only with its architecture but also its owners and its place in a particular Melbourne culture of the 20th century.
Conceived as a working farm as well as a retreat, Westerfield's grounds are planted with the eucalypt species Grimwade cultivated and recorded in a photographic study. With his friend Charles Lane-Poole, first Principal of the School of Forestry at Canberra, Grimwade was ahead of his time in matters of conservation and land use, seeking a workable alliance with industry. During the war, the property was given over to growing crops for medicinal drugs; poppies, lavender, foxglove and belladonna. The house, garden and grounds are included in the classification of Westerfield which is considered to be of national significance.