North Yorkshire Police confirmed that they removed the dressed stone from the top of the wall that surrounds parkland near the village of Forcett, near Richmond, that is part of the Forcett Hall estate.
The theft, which is being treated as a heritage crime, was reported on June 3 but could have taken place days earlier..
It was discovered by Forcett Park owner Paul Hodgson, managing director of Dales ice cream parlour Brymor - who now fears that the operation was a 'job to order' and that the criminals could return for more of the 300-year-old stonework.
Mr Hodgson's land includes 228 acres of woods, parkland and a lake, though the Grade I-listed Forcett Hall is owned separately.
"The wall is three miles long all the way around and 7-8ft high. It has these lovely round top stones. The area where the theft happened is one of the quietest corners near some woods at the southern tip.
"My concern is that they will try to come back for the rest. They jumped over the wall - there is an ancient Roman fortification that runs along it so the ground is higher behind it. They pushed the stones off and two men put them into a van. We think they did it in two stages.
"The stone is irreplaceable and the wall is unique. The police think it was bought to order for a job. They were very helpful, sent someone straight out and they found a pair of gloves at the scene.
"It's quite a quiet lane and there's no CCTV coverage. I've been setting my alarm early and driving around, and we're going to put cameras up - to catch lowlife as well as wildlife."
Police are now appealing for information and dashcam footage which could have captured suspicious vehicles or plant machinery.
Sergeant Mark Wood of Richmond police said: “This is a heritage crime and the scale of the theft suggests several people have been involved.
“The sections of this wall were all hand carved and will be very difficult to replace.”
It is not the first time historic stone has been stolen in Richmondshire. Several years ago there was a spate of stone thefts in the area.
Sergeant Wood added: “Please be vigilant and if vehicles are seen or people are acting suspiciously near to sections of wall that are topped with this type of stone please report any details to the police.”
Anyone with information, including dashcam footage, should email [email protected] or call North Yorkshire Police on 101 and select option 1 quoting reference 12220095246.