How many U.S. presidents have died in office, and what were their names?

Eight United States Presidents have died in office.  Of these, four were assassinated.  These Presidents were:

William Henry Harrison, who died of pneumonia on April 4, 1841

Zachary Taylor, who died of a gastrointestinal illness on July 9, 1850

Abraham Lincoln, who was assassinated on April 14, 1865 - he died the next day

James Garfield, who was shot by an assassin on July 2, 1881 and died of complications from his injuries on September 19, 1881

William McKinley, who was also shot by an assassin on September 6, 1901 and died eight days later

Warren G. Harding, who died of a heart attack on August 2, 1923

Franklin D. Roosevelt, who died of a cerebral hemorrhage on April 12, 1945

John F. Kennedy, who was assassinated on November 22, 1963