Major William Mills served with Loyalist forces at the Battle of Kings Mountain on October 7, 1780, where he was wounded in the leg. He served under his father Lt. Col. Ambrose Mills who was the senior Loyalist officer captured by the Patriot forces at the Battle of Kings Mountain and was hanged at Biggerstaff farm with eight other Loyalists who had been captured.

William Mills had served earlier in the War, in 1776, with the Patriots in the Cherokee Wars. He was paid as a private in Porter's Company from Tryon County for 71 days of service from Oct 21st to Dec 30th under Gen. Rutherford. The order for pay was entered in 1777.

William Mills' family was of English descent and, once the War became against the English Crown, he chose to remain loyal to the Crown.

William Mills is said to have avoided capture after the Battle of Kings Mountain by playing dead while the Patriots were collecting prisoners and escaped to Sugar Loaf Mountain, in what is today Henderson County, where he hid in a cave for a period of time. He sent emissaries back to the Committee of Public Safety for Rutherford County offering to serve the balance of the War with the Patriots. He was seeking to save his land (located back near Mills Spring, which had been named for his father) and have it exempted from confiscation by the new government.

William Mills was politically nimble. Buncombe County was formed in 1791 and included almost all NC land west of the Continental Divide William Mills' lands, now part of Henderson County, were then in Buncombe. By the time of the first census of Buncombe County in 1800, Mills had the largest labor supply in the county in the form of 20 slaves. But, Mills never held political office, probably because of his loyalist activities during the War.

Mills was credited by Sadie S. Patton in her 1947 book "The Story of Henderson County" with being the first white settler in what is now Henderson County, NC. It is not known whether he was the county's first white settler, but it is true that, when he fled to Sugar Loaf Mountain in 1780, after his Tory activities, there were few, if any, white settlers in what is today Henderson County.

Land entries in what was termed the Western Waters (across the continental divide) were first opened up in mid 1783. Charles McDowell was one of the first entry takers. The sixth entry he accepted was from William Mills for an entry of a tract of land on the west side of the French Broad River at the mouth of a large creek known as "Mills Creek". It is probable that the location was at the mouth of what is today known as Mills River. Family tradition was that he grazed livestock in that area which were probably branded and free ranged until ready for markets to the south.

The apple industry is today the major industry in the area where his lands were located. In 2013, Henderson County produced 65% of the apples sold from North Carolina. Mills has been credited, by some historians, as being the first settler to plant apple trees in the area. But, even if this is true, apples would not have been a major commodity for him on his farms. Apples are perishable and, other than as cider, could not be marketed extensively before refrigeration. In the time of William Mills which predated rail transportation, the major agricultural commodity produced in the mountains of NC was livestock which was driven on foot to the Charleston SC markets. Mills lands were located on the eastern end of the Blue Ridge Escarpment and he may have produced corn and other feed for sale to farmers fattening livestock as it was droved to South Carolina markets.