It was a bloodbath for Democrats in 2010.
From a report at the link below:
Not only did the party lose control of the House of Representatives and six seats in the Senate, the GOP picked up just shy of 700 state legislative seats, controlling 56 of the 99 chambers throughout the country. Adding to their gains in the states, Republicans also picked up six governorships in 2010, cementing their advantage.
But it wasn't just the breadth of Democratic losses that made them so damaging for the party; it was also the timing.
Following the 2010 census, the nation's congressional districts were reapportioned, and so were state legislative districts across the country. And it was Republicans who controlled the mechanisms by which those districts were drawn in many states.
Full report here.