In the Connections page in Census, click the Add Service button under the Service Connections section, and select Mailchimp.
You will be redirected to a page to log in to Mailchimp to authorize your account to Census. Once you enter your credentials and click the Log In button, you'll see a page like the image below, confirming you want to authorize Census.
Once you've authorized Census, you'll be redirected back to the Connections page in Census and you should see your Mailchimp connection there.
If you want to see your connections in Mailchimp in the future, simply navigate to the Profile page, and scroll down to the Connections and notifications section.
There are two mandatory fields for the Mailchimp connection: email and status.
Please note that the mandatory status field only accepts the following values:
For more details, take a look at Mailchimp's API documentation.
Object ID, any Text/Number
Update or Create