Unfortunately, there is no official announcement or confirmation from 20th Century Fox or the show's creators about a fourth season of Prison Break. The show's third season, also known as Prison Break: Conspiracy, concluded in 2009, and there has been no official word on a fourth season.
The fourth season of Prison Break, also known as Prison Break: Resurrection, premiered on April 17, 2017, on Fox. The show returned with a new storyline, set 10 years after the events of the third season.
Unfortunately, Fox cancelled Prison Break for a second time in 2017, and there are no plans for a fifth season. However, the show's creator, Paul T. Scheuring, has expressed interest in continuing the story in some form, possibly through a movie or a limited series.
If you're looking for when first aired:
That being said, here is some relevant information:
Following Episode 16, "The Sunshine State," which aired in December 2008, the show went on a four-month break. It officially returned on , in a new Friday night timeslot to air its remaining six television episodes. 3. The Broadcast Finale