Set any page to be used as the 404 error page under "Settings > Reading".

Shouldn't be any.

0.2.6

• Update per latest WordPress coding standards.
• Tested with WordPress WordPress 6.8.

0.2.5

• Tested with WordPress 4.5.2.

0.2.4

• Enable page templates for custom 404 pages.

0.2.3

• Set custom page in $wp_query->posts during template select.

0.2.2

• Even more reliable check for 404 page when a page template is used.

0.2.1

• More reliable check for 404 page when a page template is used.

0.2

• Custom 404 error page can now be set from the Theme Customizer.

0.1

• Initial release.

Search for "Custom 404 Error Page" using the standard plugin installer.

Custom 404 Error Page Settings