A list of existing and former windmills whose sites fall within Greater London, England. When built, these mills were within the counties of Kent, Surrey, Middlesex, Hertfordshire or Essex. Of those windmills known to have existed, nine remain and are preserved; as are the tide mills at Three Mills, West Ham.
Existing and former windmills whose sites fall within Greater London, England were only in the counties of Kent, Surrey
Besides Kent, Surrey, three other counties where these mills were in when builts are Middlesex, Hertfordshire or Essex. The system fails to check the list. It seems like it lacks understanding of an English sentence