Trish,
Not sure if you've managed to research this further. I come from Queen's Co (Laois), so I have some local knowledge I can pass on.
There were three workhouses in Queen's County in the Nineteenth Century, Donaghmore, Abbeyleix and Mountmellick. For Maryborough (Portlaoise), people would have gone to Mountmellick Workhouse.
Each poor law union was governed by a Board of Guardians. This board would meet and a weekly basis and minute books of these meetings were kept and many survive today. So for Maryborough you would need to consult the Minute books for the Mountmellick.
Unfortunately these minute books are only held by the Local Studies for each County, so Laois Local studies would be the place to go to determine firstly if Minute books exist for the time period you are researching, and secondly how these books can be accessed.
I know that Mountmellick Board of Guardian books do exist,but I don't know for what period, and they can only be accessed in person in Laois Local studies centre in Portlaoise. Maybe one of the librarians there can assist you further.
As another poster replied earlier. The only other establishments in Maryborough was the County Gaol, The County Lunatic Asylum and later on the County Hospital.
Maryborough Gaol opened in August of 1830, the Governors were as follows :
1830-1851 Archibald Wilson
1851-1869 James Young
1869-1871 Captain J.H. Healey
1871-1893 Arthur C. Bulkeley
1893-1902 John Condon
So your relative to my knowledge definitely wasn't the Governor there
I don't know about the other institutions.
Best of luck
Matt