Raj Odedra, a postmaster in Burghfield Common, Berkshire, hoped the postbox in Recreation Road would be painted gold to congratulate the diver.
After Royal Mail refused to paint the postbox Mr Odedra decided to place a replica in front of it.
It has since become a popular landmark for "selfies".
Mears and his diving partner Jack Laugher won Great Britain's first ever Olympic diving gold in the men's synchronised 3m springboard event.
Dozens of people have posted photos of their "postbox selfies" on the Burghfield Community Facebook page.
"It started off as a low key tribute to our Burghfield boy, but the postbox has since become really popular in the community - particularly on social media," Mr Odedra said.
"People from all over Reading to Tilehurst have come to visit the postbox and to take a selfie in front of it.
"It has really helped bring the community together to help support the success of Chris Mears and his family who live here."
Royal Mail defended its decision not to paint post boxes gold.
A spokesman said: "After London 2012, we confirmed that all 110 post boxes would remain gold on a permanent basis, with a plaque naming the athlete and their achievement.
"However Brazil, as the host nation of Rio 2016, has the honour of celebrating the games in its own way".
The home village of Olympic gold medallist Chris Mears has installed a golden cardboard postbox as a tribute to his Rio 2016 success.