It would seem the name John Thomas was common in that area:
1841 Census: Van . Llangendeirne, Carmarthenshire
John Thomas . M . 79 . Carmarthenshire
Jane Thomas . F . 76 . Carmarthenshire
Thomas Davies . M . 15 . Carmarthenshire
HO107 . Piece/Folio: 1385/6
Digital Folder: 101721354 . Image: 00216
1851 Census: Llety R Drew . Llangendeirne Gwempa Hamlet, Carmarthenshire
John Thomas . Head . M . 89 . Llandilofawr
John Thomas . Son . M . 43 (Est 1808) . Unmarried . Llangendeirne . Greenwich Pentioner
HO107 . Piece/Folio: 2472 / 199
GS Film: 101796624 . Digital Folder: 101796624 . Image: 00357
1841 Census: Lyrffynnon . Llangendeirne, Carmarthenshire
John Thomas . M . 45 . Carmarthenshire
Margt Thomas . F . 45 . Carmarthenshire
Esther Thomas . F . 15 . Carmarthenshire
HO107 . Piece/Folio: 1385/6
Digital Folder: 101721354 . Image: 00266
Strange record, no information or reference, but Family Search says it is in Llangendeirne.
John Thomas . M . 55 . Carmarthenshire
Margt Thomas . F . 55 . Carmarthenshire
Thos Davies . M . 25 . Carmarthenshire
Charles Jones..M.20.Carmarthenshire
Anne Thomas..F.40.Carmarthenshire
Mary Davies..F.15.Carmarthenshire
1841 Census: Bankyr Furnace . Llangendeirne, Carmarthenshire
John Thomas . M . 30 . Carmarthenshire
Bella Thomas . F . 25 . Carmarthenshire
John Thomas . M . 3 . Carmarthenshire
David Thomas . M . 1 . Carmarthenshire
HO107 . Piece/Folio: 1385/18
Digital Folder: 101721354 . Image: 00202
1841 Census: Minke Village . Llangendeirne, Carmarthenshire
John Thomas . M . 78 . Carmarthenshire
Mary Thomas . F . 65 . Carmarthenshire
Margaret Thomas . F . 25 . Carmarthenshire
HO107 . Piece/Folio: 1385/16
Digital Folder: 101721354 . Image: 00201
1841 Census: Dyffryn . Llangendeirne, Carmarthenshire
Robert Rees . M . 29 . Carmarthenshire
Margt Rees . F . 29 . Carmarthenshire
John Thomas . M . 35 . Carmarthenshire
Mary Thomas . F . 30 . Carmarthenshire
Mary Thomas . F . 14 . Carmarthenshire
Wm Thomas . M . 9 . Carmarthenshire
Anne Thomas . F . 6 . Carmarthenshire
Margt Thomas . F . 3 . Carmarthenshire
John Thomas . F . 0 . Carmarthenshire
HO107 . Piece/Folio: 1385/5
Digital Folder: 101721354 . Image: 00190
1841: Census: Blaenbryn . Llangendeirne, Carmarthenshire
John Thomas . M . 45 . Carmarthenshire
Anne Thomas . F . 50 . Carmarthenshire
HO107 . Piece/Folio: 1385/9
Digital Folder Number: 101721354 . Image Number: 00194
1861 Census: Blaen Y Bryn . Llangendeirne, Carmarthenshire
John Thomas . Head . M . Widowed . 69 . Llangendeirne, Carmarthenshire . Shoemaker
Lydia Thomas . Granddaughter . F . 20 . Llangendeirne, Carmarthenshire
RG09 . Piece/Folio: 4136 / 4
GS Film: 101819984 . Digital Folder: 101819984 . Image: 00007
1841 Census: Carraway . Llangendeirne, Carmarthenshire
David Thomas . M . 75 . Carmarthenshire
Anne Thomas . F . 50 . Carmarthenshire
Mary Thomas . F . 52 . Carmarthenshire
John Thomas . M . 22
Charles Stone . M . 30 . Carmarthenshire
Jane Stone . F . 40 . Carmarthenshire
John Stone . M . 10 . Carmarthenshire
Anne Stone . F . 8 . Carmarthenshire
Mary Stone . F . 6 . Carmarthenshire
Hannah Stone . F . 4 . Carmarthenshire
Margaret Stone . F . 2 . Carmarthenshire
HO107 . Piece/Folio: 1385/20
Digital Folder: 101721354 . Image: 00205
1861 Census: Tyr Berllan . Llangendeirne, Carmarthenshire
Margaret Thomas . Head . F . 63 . Llanelly, Carmarthenshire
John Thomas . M . 51 . Llanelly, Carmarthenshire . Carpenter
RG09 . Piece/Folio: 4136 / 10
GS Film: 101819984 . Digital Folder: 101819984 . Image: 00019