According to Dean in his book on The Plight of the Big Houses there was a house called Mount Vernon from the early 19th century. The streeets in this area take their name from it.
Read resolution of the Special Housing Committee of 23rd ultimo re-affirming their decision of 5th January to name the thoroughfares on the Mount Vernon Estate as follows : Mount Vernon Park, Mount Vernon Road, Mount Vernon Avenue, Mount Vernon Gardens and Mount Vernon Drive; and in addition suggesting that another thoroughfare on the Estate be named Mount Vernon Grove. With the exception of the proposal in relation to the naming of the additional thoroughfare, viz., Mount Vernon Grove the Committee authorised the City Surveyor to approve of the suggested street names. (Improvement Committee, 22nd March 1949).
We are grateful to Hugh Hamilton for providing the following information from his research:
Mount Vernon house was almost certainly named for the residence and plantation of George Washington, commander of the Continental Army in the American Revolutionary War and the first president of the United States.
The United Irishmen took inspiration from the American Revolution and the French Revolution and George Washington in particular was admired by the supporters of the movement. The person who built the house must have been sympathetic to the United Irishmen cause and named the 'house' after the first president’s residence.
Mount Vernon house was built by William Tennant (1759–1832), an Ulster Presbyterian banker and a leading member in Belfast of the Society of the United Irishmen. On the eve of the rebellion of 1798, Tennant was arrested and held on a prison ship in Belfast Lough. On 25 March 1799, the was transferred to prison in Fort George in Scotland. Tennant was permitted to return to Belfast in January 1802.
On his release from Fort George, Tennant retained sufficient capital to quickly re-establish himself in business. By 1807, he was one of the owners and directors of London and Liverpool New Traders, a partnership that commanded 12 ships. In 1809 he helped found the Commercial Bank, in which he worked until, enlarged, it became Belfast Banking Co. in 1827. He was on the Board of the Spring Water Commissioners and the Belfast Banking Company, and was vice-president of the Chamber of Commerce. Tennant eventually became the town's richest merchant and banker.