Jenna died in episode 22 of season 3 of The Vampire Diaries.
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Season 1
In the season 1 finale, Jenna is killed by Damon.
Season 2
In season 2, episode 22 titled “As I Lay Dying”, Jenna was killed by Klaus.
Season 3
Jenna died in season 3, episode 22 (The Departed).
Season 4
Jenna died in Season 4, Episode 22 of The Vampire Diaries. She was killed by Klaus in an act of revenge against Elena.
Season 5
Jenna died in season 5 of Vampire Diaries.
Season 6
In season 6, episode 8, Jenna died after being bitten by a vampire.
Season 7
Jenna Sommers died in season 7 of Vampire Diaries. She was killed by Damon Salvatore after she tried to kill him.
Season 8
Jenna died in season 8 of Vampire Diaries.
Season 9
In season 9 of The Vampire Diaries, Jenna Sommers dies after being stabbed in the stomach by Kai.
Season 10
In season 10, episode 12, Jenna died after being stabed by Damon.