About half of all Napa County voters who cast their ballots by mail have already done their civic duty, according to the Napa County Registrar of Voters.

About 25,700 ballots have arrived by mail or been dropped off at the Elections Office on Coombs Street, a pleased Napa County Registrar of Voters John Tuteur said Thursday, as people stopped by to drop their ballots. 

“It’s ahead of usual,” said Tuteur, who expects voter turnout will be close to 90 percent Nov. 4.

About 75 percent of all ballots should be tallied by Elections Day, said Tuteur, who noted that Napa County has a record 71,500 registered voters.

The mail-in-ballots that arrived at the Elections Office before noon Sunday will be sorted, processed and counted by 8:01 p.m. Tuesday, he said. The ballots that arrive from the county’s 41 polling places should be counted by 11 p.m.

But the  mail-in ballots that arrive at the Elections Office after 12 p.m. Sunday — possibly as many as 18,000 — will be counted after Election Day, Tuteur said.

As of Thursday, Tuteur said he believed these leftover ballots could be tallied on Nov. 18 and 19, when a technician from Sequoia, the company that makes the optical scanning device used by the county elections office, returns to Napa.

The multi-step process includes sorting the ballots, making sure that voters’ signatures match those on file and opening the ballots. The processed ballots are then placed in boxes in a secured room equipped with video cameras.

The company technician is on stand-by at the Elections Office to resolve problems with the optical scanner. A machine the size of an average business office copier reads 400 ballots a minute, Tuteur said.

Tuteur acknowledged that the outcome of some close contests may not be clear by Tuesday night. But he does not want to make mistakes, he said.

For the first time, voters will be able to drop off their ballots Tuesday at drive-through windows at the Napa Valley Expo and the Elections Office, where workers will collect the ballots.

At the Napa Valley Expo, drivers will be directed to a drive-through lane. At the Elections Office, drivers will head to the alley between Brown and Coombs streets.

Napa County’s 41 polling places will be open 7 a.m. to 8 p.m.

On Saturday, Sunday and Monday, election workers will help those who vote by mail cast their ballots at assistance centers in Napa, American Canyon, St. Helena, Yountville and Calistoga.

The assistance centers will be open 8:30 a.m. to 4:30 p.m. Saturday and Sunday; 8 a.m. to 5 p.m. Monday; and 7 am. to 8 p.m. Tuesday.

The election centers are:

• Napa: Elections Office, 900 Coombs St., Room 256; and Napa Valley Expo on Fourth and Burnell streets — Enter on Burnell Street from Third Street.

• American Canyon: Public Safety Building, 911 Donaldson Way East.

• Calistoga: Cropp Building, Fairgrounds Gate 2 — Oak Street.

• St. Helena: Stonebridge Apartments’ Community Room — 990 College Ave.

• Yountville Community Hall, 6516 Yount St.