Reznor was born in Mercer, Pennsylvania, halfway between Pittsburgh and Erie, the son of Nancy Lou (née Clark) and Michael Reznor. After his parents divorced, he lived with his maternal grandparents, while his sister Tera lived with their mother. Reznor is a descendant of George Reznor, who founded the Reznor Company, a heating and air conditioning manufacturing company, in 1888. The family sold the business in the 1960s.
His grandfather, Bill Clark, told People magazine in February 1995 that Reznor was "a good kid ... a Boy Scout who loved to skateboard, build model planes, and play the piano".