In the UK, we've been getting a lot more postal ballots in elections. But some states in the US have early voting in person, as well as "mail in", or "absentee", ballots. And the turnout has been phenomenal.
Not all states permit early voting, but still over 23 million have voted, accounting for 12.5% in West Virginia, right up to 66% in North Carolina. Note, these are percentages of the 2004 turnout, not of the electorate.