"Reform UK exists to remind politicians that they forget us at their peril," read the campaign leaflet.
A "Torfaen man, born and bred", Mr Williams said: "In my rush to reach out to the electorate I clearly made an error, but I am sure people will see the funny side of it #WhereIsTorfaen.”
Reform UK was formerly known as The Brexit Party.
Also running for Torfaen are:
Lyn Ackerman - Plaid Cymru - The Party of Wales
Veronica Kathleen German - Welsh Liberal Democrats
Thomas George Harrison - Ukip Scrap the Assembly/Senedd
Lynne Neagle - Labour
Ryan Thomas Williams - Gwlad - The Welsh Independence Party