To create a 404 page create a page whose path matches the regex ^\/?404\/?$ (/404/, /404, 404/ or 404), most often you’ll want to create a React component page at src/pages/404.js.

Gatsby ensures that your 404 page is built as 404.html as many static hosting platforms default to using this as your 404 error page. If you’re hosting your site another way you’ll need to set up a custom rule to serve this file for 404 errors.

Because Gatsby creates this page for you by default, there is no need to configure it in your gatsby-node.js file.

When developing using gatsby develop, Gatsby uses a default 404 page that overrides your custom 404 page. However, you can still preview your 404 page by clicking “Preview custom 404 page” to verify that it’s working as expected. This is useful when you’re developing so that you can see all the available pages.

The screenshot below shows the default 404 page that Gatsby creates. It also lists out all the pages on your website. Clicking the “Preview custom 404 page” button will allow you to view the 404 page you created. Gatsby Default 404 Page

The screenshot below shows the custom 404 page. Gatsby Custom 404 Page