Construction work is now under way on the £500k investment in Tullaghoge Fort, meaning the historic attraction is now closed to visitors.
The work, which began on December 1, will improve visitor access arrangements to the monument, including a car park and interpretation area.
The hill-top site, which was where the Kings of Ulster were made, has previously turned up some very important finds.
It is hoped this scheme will ensure the protection of rare and important buried archaeological remains discovered during pre-development works earlier this year.
Environment Minister Mark H Durkan said: “This project will be a boost for Cookstown.
“Enhanced visitor facilities at Tullaghoge Fort will raise visitor numbers to this area, resulting in an economic boost for tourism and local businesses.
“Earlier this year I visited the site to see the newly-discovered archaeological remains near Tullaghoge Fort. I am pleased the revised plans will preserve the integrity of this internationally important monument,” he added.
“Now that we have obtained planning permission work will start right away.
“For health and safety reasons, it will be necessary to temporarily close the site to the public, but the works will be completed in 2016 in time for the 400th anniversary of the death of Hugh O’Neill, often known as ‘The Great O’Neill’.”
Speaking about the significance of the latest archaeological finds at Tullaghoge, Mid Ulster Council Chair Linda Dillon, said: “Tullaghoge Fort is an important ancient monument and the start of construction works, which will allow visitors to enjoy enhanced interpretation at this site, is to be welcomed. The revised scheme achieves the balance of protecting our heritage and enabling the economic benefits for the wider area. I look forward to seeing the plans realised in 2016.”