The Lancaster County Sheriff's Office informed NFL Media that Dennard reported to jail March 1 and served 35 out of the 60 days in his sentence.
The Associated Press reported last month that Dennard was to serve at least 35 days after credit for good behavior and three days he had already spent in jail.
Dennard was initially sentenced to two years of probation, 30 days in jail and community service following a felony conviction for punching a police officer outside a Lincoln bar mere days before the Patriots selected him in the seventh round of the 2012 NFL Draft.
However, the 24-year-old cornerback violated his probation when he was arrested again in Lincoln on suspicion of drunken driving in July of last year, and a judge subsequently extended the probation period by an additional year and doubled the amount of jail time.
Per The AP, the drunken driving charge was dismissed in return for Dennard pleading no contest for refusing to submit to a chemical test.
Dennard played in 13 games in 2013, starting nine contests. The second-year cornerback, who attended Nebraska, picked off one pass and amassed 40 tackles last season.
The Patriots will begin their offseason training program on April 21, with organized team activities scheduled to start May 27.