Heather Basten, 29, and Travis Husniik, 33, were pulled over by officers in Wisconsin on a DUI charge on August 3, and were being driven to Oconto County Jail.
But the deputy driving the police cruiser noticed the couple having sex in the back seat and stopped the vehicle.
Husnik , who was sentenced to 90 days in jail, was told to sit in the front seat for the rest of the journey.
Sheriff Mike Jansen said: “In my 37 years on the job, I’ve not been made aware of anything like this happening in our county.”
Basten was imprisoned for 48 days, on top of being ordered to pay fines and court costs.
Judge Jay Conley, who oversaw proceedings, was reported to have said: “The process of being arrested is supposed to be somewhat unpleasant... and you end up having a tryst. Incredible.”