2004 United States state legislative elections

Elections to state legislatures were held on November 2, 2004, alongside other elections. Elections were held for 85 legislative chambers, with all states but Louisiana, Mississippi, New Jersey, Alabama, Maryland, and Virginia holding elections in at least one house. Michigan and Minnesota held elections for their lower, but not upper houses. Six chambers in three territories and the District of Columbia were up as well.

The 2004 elections created narrow legislative divisions across the country. Both parties flipped seats and chambers across the country, with most Democratic gains coming from the Northeast and West and most Republican gains coming from the South. Over 20 states featured statehouses controlled by fewer than four seats, and nearly 30 states featured divided governments. Both parties took advantage of heavy spending from 527 organizations.

Republicans won control of four chambers from the Democrats. The institution of term limits contributed to the Republican takeover of the Oklahoma House of Representatives for the first time since 1923, and favorable redistricting aided Republicans in winning the Georgia House of Representatives (and a trifecta) for the first time ever. Republicans additionally won the Tennessee Senate, for the time since 1870, and the Indiana House of Representatives.

Democrats performed better than Republicans overall at the state-legislative level, despite their defeat in the concurrent presidential election, winning control of eight additional chambers. Favorable redistricting enabled the Democratic takeover of the Montana Legislature and their retaking of control of the North Carolina House of Representatives, which was previously tied. Additionally, they took control of the Washington Senate; the Oregon Senate, which was previously tied; both houses of the Colorado General Assembly for the first time since 1963, and the Vermont House of Representatives. The Iowa Senate became tied after previously being controlled by the Republicans prior to the election. Democrats' takeover of the Montana House only came after the Montana Supreme Court declared a Democrat a victor in a contested election that evenly split the chamber. This gave Democrats control of the chamber with the help of incoming governor Brian Schweitzer.

The Democrats also regained the title of holding the most legislative seats across the country, winning one more seat than the Republicans.