Here are the deadlines in October for 24 states. You can register online in all these states:
Kansas, Maryland,* Minnesota,* New Jersey, Oregon, Virginia, D.C.,* West Virginia
Louisiana, Wisconsin,* Massachusetts
Alabama, California,* Pennsylvania, Michigan*
Utah,* Colorado, Connecticut*
*You can register to vote in person on Election Day.
For same day registration, you’ll need a current driver's license or ID card in all states to verify residency. In some states, documents such as a paycheck or utility bill with an address is acceptable for proving residence. A few states also permit an already-registered voter to vouch for the residency of an Election Day registrant.
All of the same day registration states also require that voters who register and vote on Election Day present documentation to verify their identity. Some states require a photo ID; others accept IDs without a photo.