In 1879 Edward Umfreville Blackett married Florence Rachel Theresa Laura Cleland in Belfast, Ireland. Florence was the daughter of John Cleland of Stormont Castle, then just outside the boundaries of Belfast. The Stormont estate had been in the Cleland family since the early 19th century, but it was John Cleland who substantially enlarged the original house in 1858, following which it became known as Stormont Castle. The Clelend family ceased to live at Stormont in 1893 and the estate was let.
In 1921, following the Government of Ireland Act 1920 which partitioned Ireland, the Stormont estate was purchased as a site for the Parliament of Northern Ireland. Stormont Castle itself was for 50 years the official residence and/or offices of the Prime Minister of Northern Ireland and is now the main meeting place of the Northern Ireland Executive. In 1932 the much grander Parliament Buildings were completed in the grounds of the Stormont estate. They now act as the seat of the Northern Ireland Assembly.