How often do you file federal form 940 and 941?

Form 941 is filed quarterly.

I'm not sure about Form 940; it MAY be obsolete.

Form 940 is the annual Employers Federal Unemployment Tax Return. It is filed annually and it is NOT obsolete. You must file it or you may end up with penalties for failing to file.

Mobea is correct. It's been awhile since I have done employment tax filing and I simply could not remember.