Claim: The 34th Street–Hudson Yards station (built in 2015 as part of the 7 Subway Extension), was the first station to open on the IRT Flushing Line.
Evidence: The Interborough Rapid Transit Company (IRT), a private operator, had constructed the section of the line from Flushing, Queens, to Times Square, Manhattan between 1915 and 1928. A western extension was opened to Hudson Yards in western Manhattan in 2015, and the line now stretches from Flushing to Chelsea, Manhattan. 
January 21, 1928 Opened Station Flushing–Main Street