There’s been a slow, steady shift toward using mail in elections. From 2000 to 2010 the number of votes cast by absentee ballot or in all vote-by-mail elections doubled, according to the Census Bureau and the Election Assistance Commission. A look at the states that offer vote-by-mail, when they adopted it and the growth of mail voting:
Across the U.S., 21 states allow all vote-by-mail elections in some form, meaning the entire election is held by mail. It’s especially popular in the West, where polling places are few and far between, and Oregon and Washington hold all elections entirely by mail.