Dean Koontz was born and raised in Pennsylvania. His childhood was filled with turmoil and abuse, his father being an alcoholic who was prone to violent outbursts and was eventually diagnosed as being mentally ill. Koontz, being an only child with a mother who was prone to illness, developed his own survival strategies to cope with the horrors of his home life. Books became a large part of this, as he found that they could take him into a better world. As a child Koontz desired to create this same escape for others, to give them a world to step into when their own became too harsh. Most of his novels written later contained characters who were or had been troubled children, as well as the underlying theme that that those who embrace friendship, love, faith and an unwavering commitment to freedom will inevitably win out over those who are motivated by power, envy, and greed.

Koontz received no encouragement from his parents as far as writing was concerned. They considered books and reading to be a waste of time and money, and actually discouraged him from reading. Undaunted by this, Koontz began selling original fiction when he was eight years old. He wrote short stories on tablet paper and sharpened them up with colorful covers, stapled the left margin of each story, put electrician's tape over the staples, and tried to peddle them to relatives and neighbors, usually for a nickel a story. When he was twelve he won a wristwatch and twenty-five dollars in a nationwide newspaper essay competition, writing on the subject "What being an American means to me". He realized early the need to charge a fee for his work in order to be taken seriously.

As a senior in college Koontz won a fiction competition, and wrote consistently from then on.
His first 'real' fiction sale was called "Kittens" which he sold while still in college at the age of twenty. He

Koontz wrote when he could - nights and weekends - and continued this as he left the poverty program and started teaching in a suburban school district near Harrisburg. After teaching there for about a year and a half, Koontz's wife, Gerda, made him an offer too attractive to refuse: She offered to support him for a period of five years, so that he could pursue his freelance writing full-time. "…if you can't make it as a writer by that time, you'll never make it." She told him. Of course Koontz made full use of those five years and by the end of that time his wife had quit her job in order to run the business end of her husband's galloping writing career. By this time Koontz had published a great deal of science fiction, both short stories such as "Unseen Warriors" (Worlds of Tomorrow1970) and novels like "The Haunted Earth" (Lancer Books, 1970) and "Demon Child" (Lancer Books, 1971).

Among the writers who influenced Koontz , John D. Macdonald stands among the top of the list. Koontz refers to Macdonald as a "brilliant writer" and, speaking of works he has read of Macdonald's, said "When I read something like 'Slam the Big Door', 'Cry Hard Cry Fast', 'The Damned', or 'The End of the Night', I usually turn to the last page thinking, "O.K. Koontz, face it, you don't belong in the same craft as this man; go learn plumbing, Koontz get yourself and honest trade!". His respect for writers of this caliber obviously played a part in his severely critical view of his own work. Koontz is an admitted obsessive-compulsive, and this personal characteristic drives him to accept nothing but high quality work from himself. A novel normally takes him from five months to a year to complete, and he often works seventy hours a week.

In 1976 the Koontz's moved to southern California, where they presently still reside.