In August 1818 he purchased at public tender the 10,262 1/4 acre former royal forest of Exmoor and began what became the largest single land reclamation project in England. The Forest of Exmoor had been sold by King George III's Commissioners of Woods, Forests and Land Revenues. He had a connection with the area as his aunt Mary Knight was the wife of Col. Coplestone Warre Bampfield (d.1791) of Hestercombe, Somerset, the nephew of Sir Coplestone Warwick Bampfylde, 3rd Baronet (c. 1689-1727), lord of the manors of Poltimore and North Molton, both in Devon. Col. Coplestone Warre Bampfield was a great-grandson of Sir Coplestone Bampfylde, 2nd Baronet (c. 1633-1692). The manor of North Molton is adjacent to the east side of the Forest of Exmoor and the Bampfylde family had certain valuable ancient grazing rights over the forest. Knight later increased his Exmoor estate to about 20,000 acres by purchasing surrounding land, particularly the so-called allotments which had been granted by the royal commissioners to the principal adjoining landholders to compensate them for the loss of their ancient rights over the royal forest. He built a stock-proof stone-faced wall or hedgebank around the whole estate, nearly 29 miles long, together with about 22 miles of public roads, and commenced the great task of reclaiming the rough grazing of the high moors, all over 1,000 ft, to arable production, and built two farmsteads, Honeymead and Cornham, to the east and west respectively of his own residence at Simonsbath House, Simonsbath, formerly the only residence on the forest, built by James Boevey (1622-1696) in 1654, which already had enclosed farmland of 108 acres.