X-Patents are the patents issued by the United States Patent and Trademark Office (USPTO) from July 1790 to July 1836. These patent records were burned in the Great Fire of 1836 when the facility where the records were temporarily stored caught fire.
A new facility was being built to store the records, and the existing records were stored in a temporary storage facility. The records were destroyed when the temporary facility caught fire. The U.S. government had issued about 10,000 patents by then. Most of these records could never be revived again. Congress tried to restore those records that could be reconstructed from private files. Some models that were critical were reproduced. Patents whose records were not restored were cancelled. Around 2,845 patents were restored, and most of these records were given a number beginning with "X". X-Patents bear numbers that range from X000001 to X011280. X0000001 is the first patent, issued to Samuel Hopkins in 1790.
Patents issued after the date of the establishment of the Patent Office in July 1836 were numbered without a ‘X’ in the beginning. Some of the new series patents were also destroyed in the great fire but they were soon recovered from their owners.