Some voters reported waiting hours to cast their ballots at one of the county's 10 early-voting locations open this weekend.
At one location in Culver City, for example, an hour after the polls closed at 4 p.m. there were still hundreds of people in line. Those at the end of the line weren't expected to be able to cast their ballots for another two hours after that.
LA County sees long lines at early-voting sites
The county opened 10 locations for early voting this weekend and last weekend. More than 6,000 were expected to show up Sunday alone.
And the interest in this year's midterms is seen across the state, where more than 19.6 million Californians were registered. That is 78 percent of the state's eligible voters - the highest percent for a midterm election since 1950.
"I think people are more engaged, which is great to see," said voter Alex Buchka, of West Los Angeles. "Midterms don't usually have a great turnout, so I think it's exciting that so many people are coming out."