Its a little tricky but possible. You would have to get permission from his deportation officer at ICE-Detention and Removal at the Denver District Office on Paris street I recall unless they moved. I haven't been there in several years. Then, you would have to write to the warden of the Denver Contract Detention Facility which will usually defer to ICE. So, then you would have to find an official who would be willing to perform the services at the Denver Contract Detention Facility. I would start with the warden and write him/her or visit the facility and ask for the policy/procedure and than follow that. Since he is already in deportation proceedings, you have a higher burden in proving that the marriage is legitimate and not intended to prevent his deportation.
Were you living together in Colorado at the time of his detention? And did you already consider yourselves husband and wife, and holding yourself out to the public as man and wife? If so, you may already be in a legally valid common law marriage in the state of Colorado, which will be recognized by the federal government for immigration purposes.
If not, then you should be able to arrange things at GEO for a marriage while in detention. This is assuming that your boyfriend is in removal proceedings. If he already has a removal order, and then came back to the U.S., then ICE will simply reinstate that old removal order without giving your boyfriend a second chance to see an immigration judge--and that process moves so quickly that you probably wouldn't be able to arrange a marriage in time.
If you don't mind me asking--is your intent to get married related to a possible defense to his removal?
Yes, it's possible, but if getting married is related to trying to stop the deportation, you may have issues with timing, as well as proving that yours is a real marriage. Get an experienced deportation defense attorney involved so you can have a realistic idea of what's possible.
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