I don't think you'll find Dolwenith in the 1841 census.I've looked at the properties close by it in 1851,such as Tir Bach,Tal Garnedd,Dol Ifan(or Evan) and found them on the 1841 census,but no sign of a Dolwenith.There ia however a Dol y Fellin in this sequence,occupied by a Griffith Williams.There is plenty of scope for confusion because Dolwenith in 1851 is occupied by a Griffith Thomas,with wife Anne,but the son is given as Thomas Williams!
Regards
Roger