Sheriff Mike Williams said the officer was responding to a crash on I-295 at 4:30 a.m., when the officer hit a tree.
The officer was transported to a local hospital where he later died.
"It's a tough day for JSO and the city," Williams said.
JSO said the officer worked the midnight shift. Police said next of kin has not been notified yet.
Williams believes weather may have played a factor in the crash.
MORE: Photos from the deadly crash scene
The director of JSO patrol and law enforcement, Mike Bruno, said the community's heart is saddened and describes the officer as a hero.
"Heroes are the individuals that, every day, pin on the badge or put on the uniform, knowing they might not come back, but go out anyways," Bruno said.
JSO said the officer was killed on Police Memorial Day.
"It's another reminder of the risks that men and women of JSO take on everyday when they come on this job,'' Williams said.
The Florida Highway Patrol is investigating the crash.
.@FLAnnScott and I are heartbroken to hear that a @JSOPIO police officer has passed in a vehicle crash this morning. We ask all Floridians to join us in praying for this officer’s family and loved ones during this terribly difficult time.
— Rick Scott (@FLGovScott) May 15, 2018
I mourn. Our city mourns. Sheriff Williams called me before sunrise as details were unfolding. This is sad/terrible news. Prayers for the family and all the men and women that protect us. Your city stands with you. https://t.co/eFg30rcOMt
— Lenny Curry (@lennycurry) May 15, 2018
On this Police Memorial Day, the Jacksonville Sheriff’s Office lost one of our own in a police vehicle crash.
— Jax Sheriff's Office (@JSOPIO) May 15, 2018
Please keep their family, co-workers, friends, and fellow officers in your prayers.
As more information becomes available, it will be released. pic.twitter.com/xGh3q1xhz7
Our hearts are breaking as we work a police vehicle crash at I295/Alta involving a JSO police officer who has died this morning.
— Jax Sheriff's Office (@JSOPIO) May 15, 2018
#anjaxbreaking pic.twitter.com/dlxJbazon9
— Cole Heath (@ColeANjax) May 15, 2018
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