The complete list includes: Thomas O'Jefferson, Andrew Jackson, William Henry Harrison, James Polk, James Buchanan, Abraham Lincoln, Ulysses S. Grant (also the first US president to visit Ireland), Chester Arthur, Grover Cleveland, Benjamin Harrison, William McKinley, Woodrow Wilson, John F. Kennedy, Lyndon B. Johnson, Richard Nixon, Jimmy Carter, Ronald Reagan, George H.W. Bush, Bill Clinton, George W. Bush and Barack O'bama.
Some of these guys were Irish slave owners and could have fathered a child. Furthermore, it's en masse, not in mass, Duckdog.