My son is 11 years old. I have been married to my husband since Nico (my son) was two weeks old. We live in Austin, TX. Nico's father has never been around and is currently in jail. We want Nico to have our last name. What is the first step in making this happen?

Contact your solicitor, his father will need to sign over his rights...

Shouldn't take long or be hard, any judge will allow an 11 year old to be adopted if A) the child wants to be and b) he has not seen his biological father and the adoptee has brought him up

I'm adopted and it only took 6 months to go through.

muslimaht,
Are you a muslim, is your husband a muslim?
I am just guessing from the username, if you are not a muslim,it doesn't matter:)

Yes, you will need to contact the father and have him sign over his rights. If he denies the request, you could get a lawyer... I don't imagine it would be difficult to get him to sign them over if he is incarcerated and will be for some time.
He signs over the rights, then your husband and you complete the adoption papers. I went through Child Adoption | Step Parent Adoption | Domestic Adoption, they complete the paperwork for you, made it quite easy.
Best of luck!
Pamela