Where is the air filter on a 2000 Ford Focus?

With your hood open, see the top of your intake? see the plastic/rubber hose attached to it, follow that back to the big square box, usually but not always located near the inside drivers fender, that square box houses your air cleaner, it will either have 4 Phillips head screws holding the top lid down, or 2-4 latches that can be popped up, remove the top cover, and behold your square air cleaner. Hope this helps.