Sir William Keith, Governor of Pennsylvania and the three lower counties, New Castle, Kent and Sussex from 1717 to 1726, wrote to the Board of Trade in London that he had found, 'great plenty of iron ore in Pennsylvania.' A 1734 publication mentions 'smelting works on the Christiana River, built by Sir William Keith...which produced large quantities of iron in the first two years of their existence but were abandoned the next year owing to the difficulty of smelting the ore.'

This scenario was repeated over and over again as one buyer after another purchased the land, discovered the quality of the iron was poor after overinvesting in the operation, and lost it in a sheriff's sale. Indeed, the sheriff must have grown weary of selling and reselling the same ground. There is even record of a sale of land which was 'salted' by bringing in good ore from another location in order to convince the buyer that he should act quickly before someone else purchased it.

J. P. Whitaker, owner of Principio Furnace in Cecil County, Maryland was the last of a long line of owners to mine Iron Hill, ceasing operations in 1884 when the ore ran out. On nearby Chestnut Hill William McConaughey followed suit from 1873 to 1884. The ore was originally formed when the igneous rock which makes up the hills, called gabbro, released iron through the weathering process. This iron combined with air and water and was deposited through seepage into the unaltered gabbro below. On Iron Hill, it was deposited in three distinct beds, one on top of another, with each bed about ten feet apart. For more than one hundred years the undisturbed hill has been slowly creating more iron ore. The acreage preserved as a county park will keep on creating; the rest of the hill is rapidly disappearing beneath new houses.