Since 1992, 160 changes in state legislative chamber partisan control occurred across the country. That includes 20 times both of a state’s legislative chambers changed partisan control in the same year (14%) and 120 times a single chamber changed partisan control (86%).
While chambers may have periodic split control, especially chambers with an even number of seats, these figures include only complete transfers of power from one major party to the other. Seventy-eight of these changes have occurred in lower legislative chambers since 1992, and 82 have occurred in upper chambers. Two chambers—the Washington Senate and Wisconsin Senate—changed control more than any others, at seven times each.
Seven years produced 10 or more changes in chamber control. Most recently, that occurred in 2014, when five upper chambers and five lower chambers changed partisan control nationwide.
Simultaneous control changes
Both of a state's legislative chambers changed partisan control during the same year 20 times—11 times from Democratic to Republican control and eight times from Republican to Democratic control. One time, in Vermont in 1992, the Senate changed from Democratic to Republican control while the House changed from Republican to Democratic control.
The most instances occurred in 2010, when six states saw both legislative chambers change from Democratic to Republican control. The Washington Times' Joseph Weber wrote at the time, "The Republican midterm wave swept through state capitals across the nation Tuesday, with historic gains in state legislative races that will give the GOP a major advantage in influencing congressional races over the next 10 years through redistricting." Republicans gained control of 22 chambers formerly controlled by Democrats that year.
Three states—Maine, Minnesota, and Nevada—had both state legislative chambers change partisan control twice between 1992 and 2026. One state—New Hampshire—had both state legislative chambers change partisan control four times between 1992 and 2026.
Individual chamber changes
Single state legislative chambers changed partisan control 120 times. Those are instances where only a state's upper or lower chamber changed control, while the other chamber's control remained the same. While the vast majority of changes in partisan control occurred as a result of regularly scheduled elections, a few occurred following changes in officeholders' party affiliations or as a result of special elections.
Six states—Colorado, Minnesota, Pennsylvania, Virginia, Washington, and Wisconsin—had more than five elections result in a state legislative chamber changing partisan control. Washington and Wisconsin had the most changes in chamber control with eight. Twelve states had no legislative chambers change partisan control. Nebraska’s officially nonpartisan legislature was omitted.
Click here to read more about changes in state legislative chamber partisan control since 1992, including a breakdown of chamber control changes by state.