Hi welsh lady,
there are 4 Henry Johns born 1838-1842 in Carmarthenshire but this is the only one in Llanelly.
1851 HO107; Piece: 2468; Folio: 272; Page: 24
Cylwrva Vach
Thomas Johns 46 yrs collier b Llanelly
Anna 47 yrs wife b Llandils
Wm 25 yrs engineer
Anne 23 yrs at home
Thomas 21 yrs invalide
John 19 yrs collier
Elizabeth 17 yrs at home
Daniel 15 yrs collier
Margret 13 yrs at home
David 11 yrs at home
Henry 9 yrs at home
children all born llanelly
best wishes
heywood