In 1880 Edwin Delevan Tillson, businessman, entrepreneur and the town's first mayor, retired from the active running of his companies. On a hill, overlooking the town his father had founded and he had help to prosper, he would build his retirement project. A 600-acre "Model Farm" called Annandale. So named after the maternal roots of his wife Mary Ann. E.D. Tillson was known as a man who wasn't afraid of new ideas, so it came as no surprise that his new project would encompass all the newest and latest ideas in farming technology. It also followed, that the new house built as a retirement home and farmhouse, would contain the latest ideas and conveniences. From steam heat to gas lighting the house became one of the most modern homes in the area.

However, it would be their decision to embrace the newest idea in interior design known as "the Aesthetic Art Movement", that would make the home truly special then and as a National Historic Site today. Taking almost seven years to complete, at a cost of slightly over $30,000, Annandale House became one of the most impressive homes in Tillsonburg.

After its completion in 1887, the house became the centre of the Tillson Family happenings, as well as, Tillsonburg happenings, a role that would change slightly with the sudden death of E.D. in 1902 and completely with the death of Mary Ann in 1911. After her death, the house would be severed from the farm property and sold. The Tillson heirs maintained the farm property well into the 1950's, while the house would see several different owners until 1928 when, Dr. Charles Van Dyke Corless purchased it.

Like E.D. Tillson before him, Dr. Corless would choose Annandale House as a retirement home, renaming it "Coniston Place", after his mining successes in Northern Ontario. Dr. Corless was an art and antique collector and it was his appreciation for the decorative details within the house that would see them preserved and maintained during his occupation, a stewardship that he would pass to his daughter Mrs. Florence Burn upon his death in 1954.

It was with the death of Mrs. Burn (1981) that a committee of concerned citizens would band together to save the house from possible demolition. Aware of the historic importance of the home to Tillsonburg, this group, known as the Annandale House Fundraising Committee, would approach the municipality with an idea. The group promised not to request any local tax dollars for purchase or restoration of the house if, the municipality would come on board in the daily operational costs of running the facility. The group also promised to turn the deed over to the town. Today Annandale National Historic Site is owned and operated by the Town of Tillsonburg, under its Community Service Department, while the approximate 1.3 million spent on its restoration has been managed through fundraised dollars.