Who were the presidents that were assassinated while in office?
Assassination attempts and plots on the president of the United States have been numerous, ranging from the early 19th century to the 2010s. More than 30 attempts to kill an incumbent or former president, or a president-elect have been made since the early 19th century. Four sitting presidents have been killed: Abraham Lincoln (1865), James A. Garfield (1881), William McKinley (1901), and John F. Kennedy (1963). Additionally, two presidents have been injured in attempted assassinations: Theodore Roosevelt (1912; former president at the time) and Ronald Reagan (1981). In all of these cases, the assault weapon used was a firearm. With the exception of James Garfield, the assassinated presidents all died as a result of gunshot. Garfield survived his shooting in July 1881, but his doctors infected the wound while trying to find the bullet, leading to his death two months later. 
Who were the four presidents that were assassinated while in office?
John F. Kennedy William McKinley Abraham Lincoln, James A. Garfield, William McKinley, and John F. Kennedy James A. Garfield Abraham Lincoln
List of United States presidential assassination attempts and plots ...
The assassination of United States president Abraham Lincoln took place on Good Friday, April 14, 1865, at Ford's Theatre in Washington, D.C., at approximately 10:15 p.m. The assassin, John Wilkes Booth, was a well-known actor and a Confederate sympathizer from Maryland; though he never joined the Confederate Army, he had contacts with the Confederate secret service. In 1864, Booth formulated a plan (very similar to one of Thomas N. Conrad previously authorized by the Confederacy) to kidnap Lincoln in exchange for the release of Confederate prisoners. After attending an April 11, 1865, speech in which Lincoln promoted voting rights for blacks, Booth decided to assassinate the President. Learning that the president would be attending Ford's Theatre, Booth formulated a plan with co-conspirators to assassinate Lincoln at the theater, as well as Vice President Andrew Johnson and Secretary of State William H. Seward at their homes. Lincoln attended the play "Our American Cousin" at Ford's Theatre. As the president sat in his state box in the balcony, watching the play, with his wife, Mary Todd Lincoln, and two guests, Major Henry Rathbone and his fiancée Clara Harris, Booth entered from behind, aimed a .44 caliber Derringer pistol at the back of Lincoln's head, and fired, mortally wounding him. Rathbone momentarily grappled with Booth, but Booth stabbed him and escaped. An unconscious Lincoln was taken across the street to the Petersen House. After remaining in a coma for nine hours, Lincoln died at 7:22 a.m. on April 15. As he died his breathing grew quieter, his face more calm. According to some accounts, at his last drawn breath, on the morning after the assassination, he smiled broadly and then expired. Historians, most notably author Lee Davis have emphasized Lincoln's peaceful appearance when and after he died: "It was the first time in four years, probably, that a peaceful expression crossed his face." Field wrote in a letter to "The New York Times": "that there was 'no apparent suffering, no convulsive action, no rattling of the throat...[only] a mere cessation of breathing'... I had never seen upon the President's face an expression more genial and pleasing." The President’s secretary, John Hay, saw "a look of unspeakable peace came upon his worn features".
Who was the first president that was assassinated while in office?
Lincoln Abraham Lincoln
List of United States presidential assassination attempts and plots ...
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Who was the most recent president that was assassinated while in office?
John F. Kennedy Kennedy
List of United States presidential assassination attempts and plots ...
https://en.wikipedia.org/wiki/List%20of%20United%20States%20presidential%20assassination%20attempts%20and%20plots
The four American presidents who were assassinated while in office were Abraham Lincoln in 1865, James A. Garfield in 1881, William McKinley in 1901, and John F. Kennedy in 1963. Additionally, Theodore Roosevelt and Ronald Reagan were injured in attempted assassinations, in 1912 and 1981 respectively.