was born in Eustis, Florida and is a graduate of Leesburg High School. He is a decorated combat Marine Corps veteran with distinguished service in the Republic of Panama during Operation Just Cause and the Middle East during Operations Desert Shield/Storm.

Sheriff Grinnell completed his basic law enforcement training at the Lake Technical Center in Eustis. He was hired at the Lake County Sheriff's Office in 1994, and has worked various job assignments to include: Criminal Investigations, Uniform Patrol, Organized Crime and Intelligence, Training Director, Community Services and Public Information.

Sheriff Grinnell holds a Bachelor's in Organizational Management, a Master's degree in Criminal Justice Administration, is a graduate of the Administrative Officers Course (111th) at the Southern Police Institute, University of Louisville, 244th session of the FBI National Academy - Quantico, VA and the Chief Executive Seminar (43rd) at the Florida Department of Law Enforcement (FDLE).

His professional affiliations include: Life member Veterans Foreign Wars, American Legion, Leadership of Lake County 2008, Educational Foundation of Lake County (Board Member), Hand in Hand Lake County (Board Member), Lake-Sumter State College Foundation (Board of Directors), The Salvation Army Advisory Board, Institute of Public Safety Advisory Board, Florida Criminal Justice Executive Leadership Institute (Former Board President).

Sheriff Grinnell and his wife of 34 years, Jennifer, have two children, Lauren and Blake.