do i need a passport to travel to san luis mexico if you are a us citizen?

yes you need a passport

you do now! they just changed it in the past year that you need it to go anywhere in mexico.

Only if you want to come back to the USA!

You will need to use it as proof that you are a US citizen so just take it cos if you don't need it that's fair enough but if you don't have it and you do need it then you will have all sorts of problems at border control.

You MUST have a passport to FLY to and from Mexico. You do not need a passport to travel to and from Mexico by Land or SEA yet. see site below and read top half of page carefully for current info.