A custom 404 page is a page with a message you create which a user sees when a page is not found. Drupal custom 404 pages are associated with your Site information.
To create a custom 404 page:
- First, create a basic page and add your message (see, How do I add a new Basic page?)
- Click Configuration, then System, then Site information.
- At the bottom of the overlay, in Error Pages there are two fields.
- In the Default 404 (not found) page enter the name of your new 404 page.
- You can also follow the same process to add a custom 403 Access Denied page.