The answer to your question will depend on where you are planning to be married.
If you have purchased a package through a hotel or resort, they should
know what you need to do to be certain that your marriage is legal. It may
include filing the information with the American consulate.
In many countries in Central and South America, a religious ceremony is
not recognized as a legal marriage. The legal ceremony takes place at the court
house, then the religious ceremony is held because the couple wants to have a
church wedding, not because it is legally binding.
I have had couples get married in Mexico, Peru, and Brazil and all chose to have
a small private wedding in this country before they left for their "real"
wedding. That way, they didn't have to have medical tests or wait for a
period of time to get a license in the other country, then go to the court
house, then have their wedding ceremony.
You may want to consider doing the same thing. Your pastor could marry you
in this country, then do it again in Mexico. If you purchased a wedding
package, check with the agency from whom you purchased the package.
Glenna Tooman, ForeverWed.com Wedding Consultant Memory Makers