| Honorific Prefix: | The Right Honourable |
| The Lord Ashtown | |
| Honorific Suffix: | DL |
| Office: | High Sheriff of County Galway |
| Term Start: | 1840 |
| Term End: | 1840 |
| Predecessor: | Sir John Burke, Bt |
| Successor: | Andrew William Blake |
| Birth Name: | Frederick Mason Trench |
| Birth Date: | 25 December 1804 |
| Alma Mater: | University of Cambridge |
| Spouse: | |
| Children: | 5, including Cosby |
| Relations: | Frederick Trench, 1st Baron Ashtown (uncle) Frederick Trench, 3rd Baron Ashtown (grandson) |
Frederick Mason Trench, 2nd Baron Ashtown DL (25 December 1804 - 12 September 1880)[1] was an Irish peer and magistrate.
He was son of Francis Trench and his wife Mary Mason, second daughter of Henry Mason, and nephew to Frederick Trench, 1st Baron Ashtown.[2]
While his claim to his uncle's title was admitted only in 1855,[3] he actually succeeded per special remainder on the latter's death in 1840.[2] Trench was educated at the University of Cambridge. He was appointed High Sheriff of County Galway for 1840[4] and represented the county as Deputy Lieutenant.[5]
On 29 August 1831, he married firstly Harriet Georgiana Cosby, youngest daughter of Thomas Cosby, of Stradbally Hall and his wife Charlotte Elizabeth Kelly (daughter of Rt. Hon. Thomas Kelly, Second Justice of the Common Pleas of Ireland).[6] Together, they were the parents of two daughters and three sons, including:[7]
After his first wife's death on 25 February 1845, he married Elizabeth Oliver Gascoigne in Aberford on 10 February 1852. She was the second daughter of Richard Oliver Gascoigne, of Parlington Hall and Mary Turner (daughter of Sir Charles Turner, 1st Baronet, of Kirkleatham).[6] He lived much of the year at Castle Oliver, which was built in 1845 by his second wife and her sister Isabella.[9]
Trench died, aged 75, at Clonodfoy (otherwise known as Castle Oliver) and was buried at the family's mausoleum at Woodlawn, County Galway, a week later. His older son Frederick having predeceased him in 1879, he was succeeded in the barony by his grandson Frederick. His second surviving son Cosby, who inherited Castle Oliver, was a soldier and magistrate.[10]