Adapted from the 1969 House Tour Guide

In 1854 Mr. and Mrs. William Cairns of Clifton, (now Wlllowmere) built an elegant house in the Jacobean Style for their daughter Ellen Eliza (b.1826) who had married Passed Midshipman Robert Stuart, Jr., USN. in 1848. The latter was commissioned midshipman in 1841, progressed thru the several commissioned grades of the era, and attained the rank of lieutenant in 1855. He resigned his commission in 1857. The house burned a-building as the result of a roofer's fire and was re-built during the following year on its original foundation. The present house dates, then, from 1855, and a letter survives, written in that year from Lieutenant Stuart, in "USS Relief", to his wife advising her concerning the selection of floor coverings and the placement of the garret rooms. The demesne is shown on the Walling Map as belonging to "R. Stuart". Lieutenant Stuart died in 1863 and, three years later, his widow married Elijah Ward, uncle of Admiral Aaron Ward, USN, of Clifton (Willowmere). Elijah Ward was born in Sing-Sing in 1816, started in business in New York City but then studied law and was admitted to the bar in 1843. Later he became Judge Advocate General of New York State and served several intermittent terms in Congress, where he sponsored much consequential legislation. He was an intimate friend of President Garfield. He died in Roslyn in 1882 and a splendid stained glass window to his memory survives in Trinity Church. Two years after his death his widow donated the Roslyn Watering Trough, in front of the Willet Titus House, to his memory. The Elijah Ward Post of the G.A.R. was so named in his honor. Ellen Ward died early in 1893 and, in 1895, her three children, all progeny of Lieutenant Stuart, donated the Ellen E. Ward Memorial Clock Tower to the village.

Following Ellen Ward's death, Locust Knoll was acquired by Mr. & Mrs. H.H.. H ogins who built a large dock to accommodate their 100' long steam yacht. The dock was destroyed in the 1938 hurricane. In 1919 a number of alterations were made by Mr. & Mrs. DeWitt A. Davidson who had bought the house shortly before. Most of the alterations to the original house appear to date from the Davidson period of ownership. In 1923 the house was sold to Mr. & Mrs. Clarence Schwerin. Mr. Schwerin was elected the first Mayor of Roslyn Harbor when the village was incorporated in 1931. In 1948 the estate was purchased by Mr. & Mrs. William J. Casey, who changed the name to "Mayknoll".

William J. Casey was Director of the CIA from 1981 to until his death in 1987. In May 1987, St. Mary's Church of Roslyn Harbor made front-page news as the location for the . Casey's funeral which was attended by President Ronald Reagan and former President Richard M. Nixon.