« Reply #2 on: Wednesday 06 January 10 12:16 GMT (UK) »
on the 1901 census, look for Glamorgan, St John, Central Cardiff, District His Majestys Prison RG13/4982 folios 157 - 160
The workhouse is Glamorgan, West Cardiff, Union Workhouse RG13/4988 folios 212 - 231.
But there are other institutions like Nazareth House depending on the age of the person concerned. On Ancestry, you can search for 'inmate' as relationship to head.

Cornwall: Allen, Bevan, Bosisto, Carnpezzack, Donithorn, Huddy, James, Retallack, Russell, Vincent, Yeoman
Cards: Thomas (Llanbadarn Fawr)
Glam: Bowler, Cram, Galloway, James, Thomas, Watkins
Lincs: Coupland, Cram
Mon: Cram, Gwyn, John, Philpot, Smart, Watkins
Pembs: Edwards (St. Dogmael's)
Yorks: Airey, Bowler, Elliott, Hare, Hewitt, Kellett, Kemp, Stephenson, Tebb