The oath of office is traditionally administered by the chief justice of the Supreme Court, but it doesn't have to be. How many presidents were sworn in by
someone else? *

The Presidents who lent their oath of office in front of other officers other than the Chief Justice of the Supreme Court were George Washington, first before the Chancellor of New York and then before an Associate Justice of the Supreme Court; John Tyler, in front of the Chief Judge of the Circuit Court of the District of Columbia; Millard Fillmore, in front of a Circuit Court Judge; Chester Arthur in his first oath, in front of a Justice of the New York Supreme Court; Theodore Roosevelt in his first presidency, before a judge of the District Court for the Western District of New York; Calvin Coolidge, first before the Vermont justice of the peace and then before a judge of the District Court for the District of Columbia; and finally Lyndon Johsnon, who due to the emergency situation due to the death of President Kennedy, swore on a plane in front of a judge of the District Court for the Northern District of Texas.

Therefore, there were 7 presidents who pledged their oath of office in front of an official who was not the Chief Justice of the Supreme Court.