(CNN) - Voters in Iowa have their first chance to cast ballots in the presidential election Thursday, marking the first battleground state to begin in-person early voting.
Idaho, South Dakota, New Jersey, Vermont and Maine all began in-person early voting earlier this month.
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Ohio, a key battleground, begins early voting next week, while other key states like Nevada, Wisconsin and Florida begin early voting in October.
Depending on state law, early voting can either be done in-person, through the mail or through an absentee ballot. Some states require an excuse for absentee voting while others are moving toward no-excuse absentee balloting. Military personnel are able to vote by email.
The latest poll, released in mid-September, showed President Barack Obama with a slight edge in the battle for Iowa's six electoral votes. The NBC/Wall Street Journal/Marist poll showed Obama with 50% of likely Iowa voters, compared to 42% who back Romney.
CNN's Allison Brennan contributed to this report.