Here is a link to the Vermont presidential election results, which are not final. They show that 6.9% of the voters cast a write-in vote, and 7.3% of the voters voted for a minor party or independent candidate who was listed on the ballot. Probably the vast majority of the write-ins are for Bernie Sanders. The Vermont Secretary of State will tally them in the near future. Thanks to Austin Cassidy for the link.
Never before have the voters of any state cast as much as 3% of their vote to any particular write-in candidate for President in a general election. The previous record had been the Ralph Nader write-in in 2000 in Idaho. He got 2.45% of the vote.