The counter, based inside the Morrisons Daily store on Castle Drive, is due to shut as part of a national move by the supermarket to close hundreds of its smaller outlets.
Local councillors say the closure would leave thousands of people without convenient access to essential services.
“There was a great response to the petition to save our Post Office in Dinas Powys,” said local councillor Chris Franks.
“We collected pages of signatures in a short time on Saturday morning. People were very concerned about the serious risk of the loss of counter service, with the nearest alternative being Penarth.”
Residents depend on the Post Office for everyday transactions including pensions, benefits, banking, parcels and licensing checks, and campaigners argue that sending people to branches in Penarth or Sully would cause significant inconvenience, especially for older residents and those who do not drive.
Plaid Cymru councillors have written to Post Office management asking for formal confirmation of the closure, details of any consultation, and information on what alternative arrangements will be put in place to maintain services in the village.
They have requested an urgent meeting to discuss options such as mobile provision, hosted counters or a new permanent site in Dinas Powys.
Petition sheets have been placed in Dinas Powys library, which is also opening specially on Tuesday evening between 6.45pm and 7.45pm for residents to sign.
Further signing events have been held outside the Morrisons shop and door‑to‑door, with sessions also being planned for Llandough residents who regularly use the Dinas Powys branch.
“We have been amazed with the response we have had in support of our campaign and our thanks go out to you,” campaigner Malcolm Phillips said in a local community post, sharing a photo of residents alongside councillors Anne Asbrey, Marianne Cowpe, Chris Franks and others.
Local MP Stephen Doughty has also raised the issue with UK ministers and the Post Office, saying he is “deeply concerned” about the impact of the closure and that the Post Office has indicated it will look for ways to keep services open locally, potentially in a new venue.
Campaigners say a peaceful protest outside the Morrisons store is being considered for this weekend and are urging residents to keep signing and sharing the petition to show the strength of feeling in the village.
