My father was deported to Mexico after a 10 year sentence for unlawful entry into the U.S. He is old and alone as he has no immediate family there. I was wanting to know how I can go about getting him back into the U.S legally? My mother passed when I was 19 and he is my only living parent.

He was deported so it might not even be possible for him to get permission.

You can always apply for him in hopes that the 10 years he has remained outside the US (typical ban period) was enough to let them review the application.

That's what I'm hoping for.

If you are saying he served 10 years in prison for unlawful entry and then was deported there is probably more to the story. That is a very "stiff" penalty for ONE unlawful entry. The circumstances of deportation are important if your father applies for legal entry. Was there a trial? Was this by Court order? Was he sentenced for a crime which included unlawful entry and then deported?

It matters.

(I'm ex-Homeland Security.)

You must be eligible to sponsor immigrant visa for him. That means you must be 21 y/o, employed with income of 125% above poverty guidelines for 3 years.

Consult experienced immigration attorney... good luck.