Michael Trent Reznor was born in New Castle, Pennsylvania, on May 17, 1965, the son of Nancy Lou (née Clark) and Michael Reznor. He is of German and Irish descent, and grew up in Mercer, Pennsylvania. His great-grandfather, George Reznor, founded the heating and air conditioning manufacturer Reznor Company in 1884. After his parents divorced when he was six years old, Reznor's sister Tera lived with their mother while he went to live with his maternal grandparents. He began playing the piano at the age of 12 and showed an early aptitude for music. His grandfather told People in February 1995, "[Reznor] was a good kid [...] a Boy Scout who loved to skateboard, build model planes, and play the piano. Music was his life, from the time he was a wee boy. He was so gifted."
Reznor has acknowledged that his sheltered life left him feeling isolated from the outside world. In a September 1994 interview with Rolling Stone, he said of his career choices, "I don't know why I want to do these things, other than my desire to escape from Small Town, U.S.A., to dismiss the boundaries, to explore. It isn't a bad place where I grew up, but there was nothing going on but the cornfields. My life experience came from watching movies, watching TV and reading books and looking at magazines. And when your culture comes from watching TV every day, you're bombarded with images of things that seem cool, places that seem interesting, people who have jobs and careers and opportunities. None of that happened where I was. You're almost taught to realize it's not for you." However, in April 1995, he told Details that he did not "want to give the impression it was a miserable childhood".
Reznor would later recall, "The first concert I ever saw was the Eagles in 1976. The excitement of the night struck a chord with me and I remember thinking, 'Someday I'd love to be up on that stage.'" At Mercer Area Junior/Senior High School, he learned to play the tenor saxophone and tuba, and was a member of both the jazz band and marching band. The school's former band director remembered him as "very upbeat and friendly". He became involved in theater while in high school, being awarded the "Best in Drama" accolade by his classmates for his roles as Judas in Jesus Christ Superstar and Professor Harold Hill in The Music Man. He graduated in 1983 and enrolled at Allegheny College in Meadville, Pennsylvania, where he studied computer engineering.