94 state legislative seats have flipped in special elections since 2010

Ninety-four state legislative seats have changed partisan control, or flipped, in special elections since 2010. Democrats have won 51 of these special elections, Republicans have won 37, and independent and third-party candidates have won six.
So far, six partisan flips have occurred in 2019—four Republican wins, one Democratic win, and one independent win.
The year with most flips was 2017 when 17 seats (14 Democratic wins and three Republican wins) changed party control. There were 16 flips in 2018—12 Democratic wins and four Republican wins—and 15 flips in 2015—five Democratic wins, eight Republican wins, and two third-party wins.
2017 and 2018 saw the largest net partisan gains in state legislative special elections as Democrats picked up 11 seats and eight seats, respectively. The largest net partisan gain favoring Republicans occurred in 2013 when they picked up five seats.
The states with the most flipped seats are New Hampshire and Connecticut. There have been 10 flips in New Hampshire—nine Democratic wins and one Republican win. Five of the Democratic flips in New Hampshire occurred in 2017 and 2018.
Connecticut has seen nine flips—one Democratic win, seven Republican wins, and one third-party win. So far in 2019, one Connecticut House seat and one Connecticut Senate seat have flipped from Democratic to Republican control.
About two-thirds of state legislative flips in special elections have occurred in state house seats rather than state senate seats. Since 2010, there have been 62 flips in state house seats (66.0 percent of total) and 32 flips in state senate seats (34.0 percent).
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