Way more hotels in Mexico are officially pet-friendly today than even a few years ago.
But, since I search for pet-friendly hotels when I do a custom trip plan, I can tell you that hotels that take pets are still few. In fact, I have redirected some clients' routes so they could stay at decent hotels with their dogs and cats. If you don't want me to do the legwork or paw-work for you, click on the Booking.com link to the right, type in your city and THEN click the "pet-friendly" filter. You will have to reset it every time you change cities.
When I traveled with my god, I mean dog, we had to sneak into most rooms. Today more Mexican hoteliers are accepting dogs and cats openly. It's no longer "don't ask, don't tell." Pet owners can come in out of the shadows.
When I make a trip plan for someone with pets, I notate what hotels I know (or have on good authority) to actually accept pets. Sometimes, even with the Booking.com gateway from my site, desk clerks can "forget."
This brings me to the point of this page on pet-friendly hotels in Mexico. On the right side of every page is a link that says, "Save on hotels in Mexico/USA with Booking.com". Click that link. I have pre-programed it to open to Mexico hotels. Choose your city (and any old date). Click "Search." On the left sidebar, scroll down past the Price and Star Rating to "Amenity." Click that and a drop-down menu appears. Check Pet Friendly and voila! there are the hotels in that Mexican town that accept pets.
If there aren't any pet-friendly hotels where you are going, you'll have to improvise. These scenarios have worked for me and countless others in the past.
Sometimes a clerk at a hotel with a No Mascotas policy will melt for a cute little dog. Other times, waving a 500 peso bill as a deposit will cause a manager to reconsider. Sometimes, you just have to sneak your friend in.
OK, if a hotel won't take your pet, go for a hotel that is styled like an American motel (where you can park your car in front) and get a room in the back. And, please, do clean up after your pet. That will help the next person.