Well, there's
this.
I'm assuming in this post that he is an American.
That is, that he's a US National, and not, say, an Aussie in gaol in Iowa.
Before anything else, there's one dealbreaker ground zero question.
Have you been there, and met him in person, within the last two years?
If no, then stop reading now.
Until you make another visit, and can reset that clock, you have nothing.
If yes, then read on.
Let's be clear about a couple of other things.
(i) Unlike Australia, marriage in the US is regulated by the States.
Iowa's rules may differ from those of, say, California, or North Dakota, or Rhode Island.
I suggest getting yourself a
lawyer in Iowa for specific advice about what is required there.
Apart from the general law of marriage in Iowa, the administrative process involving marriage
to prisoners is complex and onerous.
And, expensive. ---> You get to pay all the bills.
You can engage a lawyer there from Australia, as long as they are satisfied that you can and will pay them.
(ii) The
Alien Fiance process is driven by the American wanting to bring in the foreigner.
It's the American who has to file the application (they call it a "Petition").
However, him being a prisoner may be a problem.
You need to be crystal clear that he is even eligible to apply to USCIS from prison.
That's a question you'll need to ask an Iowa lawyer.
(iii) Separately to the above process, there is the question of an inmate in an Iowa gaol getting permission from the prison authorities to marry.
That will involve the inmate showing that the relationship is genuine.
(iv) It is not a given that you will get to stay in the US, just because you are married to an American.
(v) Assuming this all goes through, then even as your husband, he has no automatic right of entry into Australia, even if he ever gets out of gaol.
(vi) Having been convicted of something that got him gaoled, chances are, he'd never meet the Good Character Test for an Australian Visa.
Truth be, you're pushing a very big rock
up a series of very steep hills here.
But, everyone should have a chance at happiness.
Best of luck.