Marquess of Londonderry

Marquess of Londonderry, of the County of Londonderry (/ˈlʌndəndriː/ LUN-dən-dree), is a title in the Peerage of Ireland.

The title was created in 1816 for Robert Stewart, 1st Earl of Londonderry. He had earlier represented County Down in the Irish House of Commons. Stewart had already been created Baron Londonderry in 1789, Viscount Castlereagh, of Castlereagh in the County of Down, in 1795 and Earl of Londonderry, of the County of Londonderry, in 1796. These titles are also in the Peerage of Ireland.

He was the son of Alexander Stewart, who had married Mary Cowan, sister and heiress of Robert Cowan, who gained great wealth as Governor of Bombay from 1729 to 1737. Alexander was from Ballylawn, a townland at the south-west corner of Inishowen in the north of County Donegal, a county located in the west of Ulster in the northern part of Ireland. However, much of the Stewart family wealth was based on the estates which came into the family through this marriage.

...
Wikipedia