You can register for an API key, free of charge, by following these steps:

1.      Go to the Developers site

2.      Click on the Request a KEY box on the left side of the page.

3.      Fill out the pop-up window form. Make sure the email address you use to request the key has an extension of .com, .net, .org, .gov, or .edu.

4.      You will receive an email with your key code in the message and a link to register it.

Once you have a key, insert &key= followed by your key code at the end of your API data calls: &key=your key here

Your API key must also be used to access pages within the API Discovery Tool (api.census.gov/data.html?key=your key here). When accessing the metadata pages within the Discovery tool, insert ?key= followed by your key code at the end of your metadata query: ?key=your key here