If you click on the URL in the Crawl Errors report you will get a popup containing a "Linked From" tab. In that tab, Google will tell you where it found the link to those pages:
You may find that they are:
- Broken links on your site
- Broken links on 3rd party sites
- Text URLs Googlebot discovered that are not linked
Your own site crawl is only likely to find the broken links on your own site. Since Googlebot crawls the whole web and has heuristics for finding what it thinks might be links, it will find more errors than your own crawl of just your site.
Google expects properly functioning sites to have some 404 errors. In fact, Google gets worried if Googlebot never gets a 404 error for any URL, especially those that should be junk. As long as the URLs that are returning a 404 are not supposed to have content, those 404 errors will not hurt your site in any way. It doesn't matter if there are 10 of them or 10 million of them.
There are a few basic methods for fixing crawl errors:
- Remove the link to the 404 page if it is on your site
- Fix the link to the 404 page such that it points to the correct thing
- 301 redirect the 404 URL to the actual page (ex:
- Put up a new page of content at the error URL