The Wisconsin policeman driving the car noticed the pair’s amorous activity in the back seat and stopped the vehicle.
Heather Basten, 29, was already in trouble with the law after being pulled over in Wisconsin with her lover, Travis Husnik, 33, on suspicion of driving under the influence.
The couple were put in the back of a police cruiser for the ride to Oconto County Jail on 3 August.
The deputy driving the car noticed they were getting amorous in the back seat and stopped the vehicle.
He told Husnik to pull up his trousers and get in the front of the car for the rest of the journey.
The two were charged with disorderly conduct and lewd and lascivious behaviour.
Sheriff Mike Jansen told Sky News: “In my 37 years on the job, I’ve not been made aware of anything like this happening in our county.”
Husnik was sentenced to the maximum 90 days in jail because of his criminal record.
Basten received 48 days, plus fines and court costs.
Assistant District Attorney Robert Mraz said the couple’s behaviour was “a little disgusting”.
Judge Jay Conley was quoted by the Green Bay Press Gazette as saying: “The process of being arrested is supposed to be somewhat unpleasant … and you end up having a tryst. Incredible.”