(NEXSTAR) — Election Day is nearly upon us, meaning millions of Americans will be heading to the polls to cast their vote.  Depending on where you live, you may have had to register a month ago. Or, maybe you’re among the millions who live in a state that allows you to register to vote moments before you cast your ballot.  Twenty states and the District of Columbia allow voters to register on Election Day.  In most cases, in-person registration is the only applicable method. However, in Hawaii and Vermont, residents are also able to register online on Nov. 5 before heading to the polls.  In Maine, same-day registration is only available online: the last day to register by mail or in person was Oct. 15.  Below is a list of states that allow in-person, same-day voter registration:  California Colorado Connecticut District of Columbia Hawaii Idaho Illinois Iowa Maryland Michigan Mississippi Montana Nevada New Hampshire New Mexico Utah Vermont Virginia Washington Wisconsin Wyoming What you need to bring to register may vary slightly by state.  You’ll need your driver’s license, a state ID card or your Social Security card in California, Colorado, Hawaii, Maryland and Washington. An ID showing your current address is enough in Iowa, but if the address is no longer accurate, you’ll need to bring another document to serve as proof of residence. Mississippi requires only a photo ID, while Nevada will only accept a valid state driver’s license or ID card.  In Wyoming, you'll need a photo ID to register, or at least two other documents that “constitute proof of [your] identity.” Other states are more broad about what proof of residence is acceptable. In Connecticut, you’ll need a copy of a valid photo ID, like your driver’s license or a state ID, or a copy of a current bill, bank statement, government check, paycheck or a government document with your name and address. States with similar lists of acceptable proof of residence guidelines include Michigan, Montana, New Mexico, Vermont, Virginia and the District of Columbia.  Some states require two forms of identification. In Idaho, you need a photo ID and proof of residence. An applicable photo ID could include not only your driver’s license and state ID, but your passport, a federal ID, a tribal ID card or a concealed weapons license issued by a county sheriff. Your proof of residence could be any of those identification cards or the aforementioned bills or documents with your address on them. Utah has similar requirements. Illinois calls for two forms of identification, with at least one showing your current home address. While you need a photo ID to vote in Wisconsin, you don’t need one to register to vote. You do, however, need a proof of residence document. In New Hampshire, you need to prove “your identity, age, citizenship, and domicile” to register. The state lists multiple forms of identification that can prove some or all of those requirements.  Many states use provisional votes when it comes to same-day voter registration. These ballots are not counted until your identity has been confirmed. Your vote will still count (if you are who you say you are), but may not be counted until after Election Day. Be sure to check with your local elections official to ensure you have what you need to register to vote. It’s important to note that you may not be able to register to vote at your polling place. Instead, you may need to go to an office dedicated to handling these requests. You can find that information from your state or county elections office.