After-hours voting lasted more than two hours at Dayton High School in Lyon County.
In Reno, the last voter cast a ballot at a shopping center, one of Washoe County's 82 centralized polling places, at nearly 10 p.m.
"We did not expect the ... incredible midterm turnout," county Registrar of Voters Deanna Spikula said of the record 70 percent of registered voters who cast early and Election Day ballots in the Reno area. Spikula said officials in northern Nevada's most populous county had planned for 60 percent turnout.
Authorities didn't field reports of fraud or illegal activity during midterm elections, said Wayne Thorley, deputy Nevada secretary of state.
The state last year replaced aging voting machines in 16 counties with upgraded machines that print and store a paper copy of the electronic vote, Thorley said. Carson City uses a different electronic system that prints a ballot that the voter hands to a poll worker.
There was no immediate indication the changeover was responsible for the lengthy delays, Thorley said.
Statewide, 62 percent of the Nevada's eligible voters chose a new U.S. senator and governor, as well as decided other races including for the U.S. House, six ballot questions and seats in the Legislature.
But the outcomes on all those races were delayed more than three hours as election officials waited for the last vote to be cast before releasing any results.
In Las Vegas, where the longest lines stretched more than two hours, one Republican Party poll observer attributed delays to the sharp reduction in the number of polling places since 2016, an underestimation of voter turnout and a policy change that let people in four of the state's most populous areas — Clark, Washoe and Douglas counties and Carson City — vote anywhere they wanted.
Previously voters had to cast election day ballots at designated precinct polling places.
Clark County, home to three of the state's largest cities and seven in 10 of the state's voters, went from 272 polling places in 2016 to 172 at-large vote centers on Tuesday. More than 223,000 voters cast Election Day ballots in the Las Vegas area.
Kulin said voter volume caused the delays, and Thorley called it premature to conclude that a reduction in polling sites in Clark County caused long lines.
However, "This was the first time where you could vote anywhere in the county instead of your own precinct," said Erven Nelson, a lawyer and former Nevada state Assemblyman who monitored polling stations in Las Vegas.
"I think it was a combination of people waiting until after work to go to the polls and equipment malfunctions like running out of paper," said Nelson, who watched voting continue until nearly 8 p.m. at an elementary school that provided 10 voting machines for most of the day.
In the evening, vote machine printers ran out of paper, and the site only had six backup printers, Nelson said. Four machines were idled during the hour it took for the line of voters to cast their ballots.
A similar problem occurred at a Las Vegas high school where voters waited in line for two hours. Election officials had to deliver more printers, Kulin said.
The 17 counties are due to submit reports about their elections to the state by Jan. 7, Thorley said. "As we go through the postelection processes, we will work cooperatively with the counties to identify areas to improve," he said.
Spikula, in Reno, said two sites with long lines after 9 p.m. were in Cold Springs and Sun Valley, two fast-growing areas north of Reno. In the end, everybody who wanted to vote did, she said.
"Can we do better in the future?" Spikula said. "Yes, we can."