The Prince of Wales's Duchy of Cornwall estate has received more than £1 million over the last six years from people in the county who died without making a will or having an heir.
Historic constitutional powers meant the Duchy is entitled to all unclaimed property and estates left when someone dies in Cornwall.
Known as bona vacantia, the legal term for ownerless land, the powers date back to the creation of the Duchy of Cornwall estate in 1337 by King Edward III.
The Duchy estate was created to provide an income for the King's son and heir, Prince Edward, otherwise known as The Black Prince, who became the first Duke of Cornwall.
Last year, a total of £552,000 passed to the Duchy under the law. Since 2006, the amount adds up to £1,019,000.
The money, though is not retained by the Duchy, but donated to charities through the Duke of Cornwall's Benevolent Fund, minus an amount for "ex gratia payments and other associated costs" – which amounted to £86,000 last year.
A Duchy of Cornwall spokesman said: "The Prince of Wales decided almost 40 years ago that the bona vacantia funds should be given to charity."
In most cases, the estates of people who die without making a will, and who have no obvious heirs, go to the Government.
The anti-monarchy group Republic, which last month launched a campaign in Cornwall to abolish the Duchy, said the bona vacantia money should do likewise.
"The money made from unclaimed property in Cornwall should go where it does everywhere else in the country," spokesman Graham Smith said.
"It should go to the Treasury and into public funds to be spent on public services."
In addition to the bona vacantia arrangement, the Duke of Cornwall also has several little-known rights and powers, including the right to veto Westminster legislation.
Last year, Prince Charles' private funding from the Duchy of Cornwall rose by 3% to £18.3 million.
His income from grants-in-aid and Government rose from £1,962,000 to £2,194,000.
In addition to vast swathes of land in Cornwall, the Duchy owns land in 22 other counties, stretching as far north as Cheshire.
The estate, which has more than 3,500 lettings, which include 1,000 commercial agreements and 700 residential lettings, also owns the Oval cricket ground.