Ron Bailey dug up the button some time ago and has been trying to learn more about its origins for some time.
Now, thanks to an article in last week's Times, the mystery has been solved.
Mr Bailey thought the brass button dated from about 1936 — it had the words 'Tavistock Volunteers' inscribed on it, with a crown and Roman numeral eight.
'Apparently it's dated from the time of George IV — Tavistock Volunteers were part of the Devon Militia at that time,' said Mr Bailey, who was contacted by a Times reader with knowledge of old buttons.
He has now sold the button to a collector in Plympton.
'It's been in my garden for the last 130 years and now it's part of a collection,' said Mr Bailey, who was delighted to find out about the origin of the button.