William Lemon was the son of a William Lemon, of Germoe, in humble circumstances; he was baptized at Breage, 15th November, 1696; his mother's maiden name was Rodda. As a lad he obtained a smattering of knowledge at a village school, sufficient to enable him to enter an office as clerk to a Mr. Coster. The story was told of him that as a boy he had formed one link of a living chain, which, connected only by the grasp of their hands, extended itself into a tremendous surf, and rescued several persons who had been shipwrecked.

Whilst still young he became manager of a tin-smelting house at Chiandower, near Penzance, and speedily acquired a great knowledge of mining in Cornwall. In 1724 he married Isabella Vibert, of Tolver-in-Gulval, and with her received a sufficient fortune[23] to enable him to indulge in speculations in mines, and these turned out so happily that he embarked still further in mining ventures. He was the first who conceived the project of working the mines upon a grand scale, and not of running them by small bands of adventurers. A new era in mining opened with the introduction of the steam-pump, and the first, invented by Newcomen, of Dartmouth, was used in the Great Work at Breage. William Lemon associated with himself George Blewett, of Marazion, and a Mr. Dewin, and these three commenced working a mine on a farm called Truvel, in Ludgvan, the property of Lord Godolphin, and named Wheal Fortune, where the second steam-engine was employed.

Mr. Lemon is said to have realized £10,000 out of Wheal Fortune, and this enabled him to extend his operations. He removed to Truro, and commenced working the great Gwennap Mines on a scale unprecedented in Cornwall. Carnan Adit was either actually commenced, or at least was effectively prosecuted, by Mr. Lemon; and as his means increased he soon became the principal merchant and tin-smelter in Cornwall.

But he was keenly alive to his deficient education. He was shrewd, could calculate, but had no knowledge of English literature, and his spelling was remarkable. However, he set vigorously to work to correct his defects, and late in life placed himself under the tuition of Mr. Conon, master of the Truro Grammar School, and even acquired a certain—not, certainly, very extensive—knowledge of Latin.

Mr. Lemon had a favourite tame Cornish chough that would always obey his call. If he were walking on Truro Green, or through the streets, the chough would fly to him instantly at his whistle, though it had been associating with other birds or perched on a house-top.

It so happened that John Thomas, afterwards the Warden of the Stannaries, but then a boy at Conon's school, taking his gun, contrary to the rules of the school, and going out shooting, unluckily killed the chough. This produced a great outcry, and when he was told that this was Mr. Lemon's favourite bird, he strongly suspected that the least punishment he would receive would be a flogging from his schoolmaster and a hiding as well from Mr. Lemon. But Thomas took courage, went to Mr. Lemon's house, knocked at the door, was admitted to Mr. Lemon, and trembling and in tears confessed what he had done. Mr. Lemon paused a moment, and then said that he was sorry for the poor bird, but freely forgave the little delinquent on account of his candour in acknowledging his fault, and more than that, he promised to keep it a secret, and if it should reach Conon's ears, would intercede for him.

In 1742 he was Sheriff for the county. He became one of the Truro magistrates, and might, had he cared for it, have been elected as a member for one or other of the Cornish boroughs.

He was author of a lucid argument written to Sir Robert Walpole to obtain the withdrawal of a tax levied on coals, and which acted prejudicially on the Cornish mines. The presentation of this memorial is thought to have been instrumental in obtaining for him, from Frederick, Prince of Wales, a grant of all minerals found in Cornwall, with the exception of tin; and the Prince likewise sent him a present of silver plate.

He bought Carclew in 1749, and died at Truro, 25th March, 1760, in the sixty-third year of his life.

He and his wife had one son only, William Lemon, junior, who died some years before his father, leaving two sons and a daughter. The elder, Sir William Lemon, Bart.,[24] represented the county of Cornwall in Parliament during fifty years.

As an instance of the respect paid to the genius, and above all the wealth of Mr. Lemon, the people of Truro are said to have drawn back from their doors and windows as he passed through the street, and the Rev. Samuel Walker, when exhorting children at catechizing to be circumspect in the presence of Almighty God, said: "Only think, dear children, how careful you would be if Mr. Lemon were looking upon you."

Sir William's eldest son, Major William Lemon, shot himself at Princes Street, Hanover Square, London, early in 1799, when a young man of only twenty-five.

The baronetcy is now extinct, and Carclew is the residence and property of Captain W. Tremayne.