Will our travel iron and hair dryer work in Mexico? The voltage is 120V but most sites say the voltage is 110!?

The US has a universal voltage of 117 volts this is due to the multi phase split of yor.
Originally Germany (and that was where US electricity came from) was 220 v split at the centre giving 110 however some wag decided that 60cycle was more efficient and so used 60 HZ. This was compounded when another wag decided that you could run 2 appliances from the same socket giving 110.
When the cycles were changed to 60Hz it became apparent that the voltage had to go up, hence 115. This was not easily complied with directly so 117 was the norm.
So anywhere that says 110 is in probability 117, and that as a result all new appliances should be marked 120V

The other guy gave a lot of verbage without answering your question.
YES--your travel iron will work. The two voltages are close enough.

Mexico has the same electrical standard as the US, devices marked 110to 120 will work just fine. The only difference is that Mexican wall outlets do not have a grounding port, so a simple adapter should take care of that if your devices have grounding prongs.

YES iT WiLL
MY Straightener WORKED iN MEXiCO1

Yes, When in Mexico the hair driers, toasters, rechargers, radios, that we got in the US have worked. Except for the hair dyer that fell out of a suitcase during customs inspection and landed on the floor, but that happened in LA airport, but that is another story.