Almost 79 million people voted in Tuesday's election, with Democrats drawing more support than Republicans for the first time in a midterm election since 1990, according to a private analysis.
The overall turnout rate, reflecting a percentage of voting age population, was 40.4 percent, compared with 39.7 percent in 2002, the director of American University's Center for the Study of the American Electorate said.
A preliminary analysis showed that turnout was down in some states and higher in others - notably up in Virginia, where it appeared more people voted than in any midterm in the state before, researcher Curtis Gans said.
The highest recent midterm turnout was 42.1 percent in 1982.
The total popular vote nationwide was 78,707,495.
In Virginia, where Democratic challenger James Webb's lead over Republican incumbent George Allen was razor thin, an estimated 43.7 percent of eligible voters went to the polls, compared with 29.2 percent in 2002, the last nonpresidential election year.
Ohioans also came out in substantially greater numbers. Unofficial figures showed 44.6 percent of eligible voters cast ballots compared with 38.4 percent in 2002.
Turnout was substantially higher in Michigan, Missouri, Connecticut and Montana; it was somewhat higher in Delaware and Kentucky.