Be aware that Frontier is currently using gates in both Terminals D and E, which are pretty far from each other, but connected by bus outside of security and by the Skylink train inside security. When flying out of DFW, check carefully to see which terminal you are departing from. It seems that, right now, Frontier only uses D gates in the morning.

I recently had a bad experience with this confusing situation. I was returning a car at the airport. The car rental center is several miles from the terminals, and they run different buses from there to each terminal. I knew I was leaving on Frontier from Terminal D, so I got on the D bus. It stopped at that terminal and everyone got off. Since I was checking luggage -- unusual for me -- I followed the signs to the ticket counters. There was no obvious Frontier ticket counter there, and no signage to go elsewhere. This surprised me because, when I checked in online, Frontier told me they had ticket counters in both D & E. I asked three different airport employees and they all told me that Frontier only had a ticket counter in E. I was skeptical of this information, but my wife preferred to just go to E, which we did by tediously then taking the Airlink bus between terminals. There, we did easily find a Frontier ticket counter, went through security (somewhat of a walk to get to a Precheck line), and took the Airlink train back to D. This wasted about a half hour of time.

I still believe it likely that there IS a Frontier ticket counter in D, because there are many int'l airlines that use that Terminal and I didn't see any of their counters either. It must be "hidden" somewhere, and DFW just does a poor job directing passengers around the airport (no announcements or information on the buses, and no signage). If anyone locates it, please post that information here. In the meantime, be aware of this odd two-terminal situation, and be particularly careful if you're arriving at the terminal area from the rental car center.

According to comments on this reddit thread, its true, there is only a desk at E.

Oh dear.

I guess it would be helpful is someone who is scheduled to fly out of DFW from Terminal D in the morning -- preferably somebody who did NOT need to check luggage and was just headed to security -- took a look to see if there is actually a Frontier ticket counter in D. Frontier sent me this email before my flight, but of course I don't entirely trust them. I suspect that if they do have a ticket counter, it's in the same place where the international airlines have counters.

BTW, if you have lounge access, it's worth noting that the AMEX Centurion lounge is in Terminal D, so that's not a bad place for your Frontier flight to leave from. That lounge opens at 5:30 am, with hot food at 6:30 am. I understand that there is a new Priority Pass lounge (Plaza Premium) in E that also has hot food, but it is reportedly small and quite crowded.