Helsinki wins the 2017 Worldcon outright on the first ballot, polling 52% of first-preference votes with a near-record turnout.
There were 2624 total ballots cast, with 2605 expressing a preference. That means that to win on the first ballot, a candidate needed 1303 votes (a majority). The major candidates received:
Helsinki: 1363
DC: 828
Montreal: 228
Nippon: 120
The remainder were write-ins and invalid ballots, not affecting the result.
Technically, these results are unofficial until received by the Site Selection Business Meeting on Sunday morning. There is no dispute about the results, however, so the receipt of the results should be a formality. However, inasmuch as both I and jared_dashoff are part of 2017 bids, we'll both recuse ourselves from presiding over that part of the meeting in favor of Donald Eastlake III, the Business Meeting Parliamentarian.