Bonerz was born in Portsmouth, New Hampshire, to Elfrieda, who was born Kern, and Christopher Bonerz. His early life took him to Milwaukee, Wisconsin, where he attended Marquette University High School. During his time at the high school, Bonerz had his first taste of the theatrical world while performing with the Prep Players.
At Marquette University, Bonerz continued his involvement in theater by participating in the Marquette University Players. After graduating with a Bachelor of Science degree in 1960, Bonerz decided to pursue a career in theater. He began his journey in New York City, initially working with a troupe called The Premise, focusing on improve.
Following his compulsory service as a draftee in the United States Army, Bonerz joined an improve troupe in San Francisco known as The Committee. This troupe, which was comprised of talented individuals, included Rob Reiner, David Ogden Stiers, Howard Hesseman, and Hamilton Camp.
