and where would be a good place to look up the question for different states
Personal Injury Lawyer
Yes, there is not legal prohibition based upon criminal record in MD or DC. Not familiar with other states.
Estate Planning Attorney
Absent any prohibition in the Power of Attorney instrument, a person who has been convicted of a felony may be named as an agent (or attorney-in-fact) by the Principal (the person creating the Power of Attorney) in Maryland. However, the instrument could be written to disqualify an agent if they are convicted of a felony if the Principal has a concern. If you are choosing to name someone who has been convicted of a felony and if there is concern among other family members, a solution may be to require that the agent provide regular accountings regarding how he/she is managing the assets/affairs of the Principal.
You should contact an attorney licensed to practice law the the applicable state to advise you specifically regarding your set of circumstances. While there are a number of research resources available, you would likely need to check each state's legal resources - such as the state code - for information this specific. I am not aware of a single resource that would address this issue in each jurisdiction.
Best of luck.