The U.S. Patent Office has almost seven million sequentially numbered patents electronically available through its online web interface. You might be surprised, however, that Patent Number 1 (Traction wheels for a locomotive) was not the first patent. The first 10,000 patents issued between 1790-1836 were not originally numbered and all records of them were lost in a fire at the patent office.
No copies of the patent descriptions and drawings were kept anywhere else, and only a copy of the official patent certificate was sent to the inventor. Patents were not numbered then; they were referred to only by name and issue date.
The patents that were recovered have been renumbered as x-patents. Thus, Samuel Hopkins’ 1790 patent for potash manufacturing is U.S. Patent No. X-1. In today’s NYTimes, Teresa Riordan has a nice article about the ongoing search for the lost patent documents.
Update: PHOSITA has a great post with more history on the Patent Office fire.