William Reynolds was born in Ketley in 1758, the oldest son of Richard Reynolds and his first wife Hannah Darby. His father was an ironmaster and philanthropist, and managed the Coalbrookdale ironworks from 1763 to 1768, during which time the young William served his apprenticeship there. He was extremely able, studying chemistry, taking an interest in geology and other sciences, and keeping a laboratory and library at his home. With his brother-in-law, he had set up a new ironworks at Donnington Wood in 1783. He developed a circle of friends from the engineers and manufacturers who visited Coalbrookdale, including Matthew Boulton, James Watt, 'Iron Mad' John Wilkinson, Thomas Telford, and a number of intellectuals connected with Joseph Plymley.