Iowa:
Any registered Iowa voter may apply for an absentee ballot and vote by mail.
https://sos.iowa.gov/elections/electioninfo/absenteeinfo.html

Minnesota:
Any registered Minnesota voter may apply for an absentee ballot and vote by absentee ballot.
https://mnvotes.sos.state.mn.us/ABRegistration/ABRegistrationStep1.aspx

Nebraska:
Any registered Nebraska voter may apply for an absentee ballot and vote by mail.
https://sos.nebraska.gov/elections/early-voting-0

North Dakota:
Any North Dakota resident may apply for an absentee ballot and vote by mail.
https://vip.sos.nd.gov/absentee/Default.aspx

South Dakota:
Any registered South Dakota voter may apply for an absentee ballot and vote by mail.
Note: State law requires completed absentee ballot applications to be notarized or include a photocopy of an acceptable photo identification card.
https://sdsos.gov/elections-voting/voting/absentee-voting.aspx