In the 46 years prior to the Great Fire of 1836, the United States government had issued about 10,000 patents. Most of these could never be revived again, but Congress acted to restore those records that could be reconstructed from private files and reproduce models which were deemed critical. Patents whose records were not restored were cancelled. There were a total of 2,845 patents restored, most of which were eventually given a number beginning with "X". All patents after the date of the establishment of the Patent Office in July 1836 were numbered as a new series (without the X), beginning with a new Patent No. 1 to John Ruggles. A small number of the new series patents had been destroyed in the Great Fire but they were quickly recovered from their owners' records. X files bear numbers that range from X000001 to X011280. X0000001 is the first patent, issued to Samuel Hopkins in 1790.
Source: U.S. Patent and Trademark Office.