A father in Arizona had sex with a 15-year-old girl he had hired to babysit his 10-year-old daughter, police said.

Joseph Peter Sisemore, 41, was arrested on Monday in the 100 block of North Dobson Road after having roughly 25 sexual encounters with the teen victim at his apartment in Chandler since November, police said.

Investigators believe Sisemore is a sovereign citizen — anti-government extremists who believe laws and taxes don’t apply to them.

Sisemore allegedly performed oral sex on the victim and had sexual intercourse with the teen. He also digitally penetrated the girl and had her perform oral sex on him as well, Chandler police Detective Seth Tyler told The Post.

All of the alleged encounters are believed to have occurred at Sisemore’s apartment and took place some two years after the teen victim was first hired, Tyler said.

“There was probably some grooming going on,” Tyler told The Post. “As parents, it’s so important to keep track of what our kids are doing. It’s so important that we make sure we know who is at the house or what type of things are being said to them.”

Sisemore was arrested after the parents of the 15-year-old girl notified police. He was taken into custody as he walked out of a drugstore after buying the morning-after pill for the victim, according to a probable cause affidavit obtained by The Post.

Sisemore also asked the girl during the alleged encounters to “wear some of his clothes as pajamas” so he could smell her on his clothing later, the affidavit states.

In 2010, FBI officials characterized sovereign citizens as people who simply believe “they don’t have to answer” to any government authority, including judges or law enforcement officials.

Sisemore, meanwhile, admitted to having sex with the teen during three separate recorded phone calls earlier this week, acknowledging that he could get “into a lot of trouble” if the encounters were uncovered, according to the affidavit.

Sisemore was taken into custody at the Maricopa County Jail on 11 counts of sexual conduct with a minor. It’s unclear if he’s hired an attorney.