If he was admitted to the US and has an I-94, then you can petition for him in the US with an I-130 and an adjustment package. If he is in Mexico, then you start with the I-130 and then he will have to finish the application at the US Consulate in Cd. Juarez.
(213) 394-4554 x0 Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.
As indicated by my colleague, this is not a straight forward question as much needs to be considered, including your husband's entry(ies) into the us, immigration background, whether he's eligible to adjust, whether he would have any bars upon departure from the US if he needs to leave to process his case in Mexico, whether he would need any waivers, etc.
You'd be wise to consult with an attorney to get a solid idea of what is and isn't possible and what you should and shouldn't do.
My office is in Houston and I handle such cases. I encourage you to consult with me or one of my colleagues.
The information offered is general in nature and not meant to be relied upon as legal advice. Please consult an attorney prior to making legal decisions. Visit us at www.tunitskylaw.com. Contact us at 713.335.5505 or email at email@example.com. Veronica Tunitsky offers in-person, as well as telephone and email consultations.