The State-Specific Voter Information Directory on this website provides voter registration and absentee ballot request deadlines for your state. You'll find a link to the directory in the main menu.
Note, deadlines vary, and not just by state. If you are already considered a registered voter, you may be able to use the Ballot Request deadline - which is often extended.
Voters should submit a voter registration application/absentee ballot request each year and whenever your overseas address or other personal information changes to keep your registration current.