US Patent Office Search of Patents for Inventions
a good starting place...
The US Patent Office (USPTO) manages the library of all U.S. Patents for inventions. The library includes utility patents, design patents, plant patents and published patent applications. Several 3rd parties use the USPTO database of patents to provide services for searching and finding patents. For example, Google has scanned U.S. Patents and provides one of the better methods for finding these documents using Google's search engine. The bottom line is that with the right knowledge and strategy YOU can do a patent search through the internet using these free resources.
US Patent Office - Search Patents and Inventions
USPTO patent search instructions
Step 1. Find your database
Go to USPTO.GOV to find the United States Patent and Trademark Office home page. The page is divided into 3 columns with the left-hand column being dedicated to information about patents and inventions. Click on item #2 "search" to go to the search page.