Most of them were holding a single sheet of paper that would ensure their vote was counted. Voters filled out that paper to request a new ballot after not receiving theirs.
"It was supposed to be mailed a week or 10 days ago, and I never received it in the mail," said Michelle Slavik of Fairmount.
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"I didn't want to take a chance. This election is too important," said Novilette Jones of Somerton.
Other voters found out there were issues with their ballots that needed to be corrected.
"I went and tried to fix it in person at my satellite office and it still hasn't updated," said Bridget O'Keefe about an ID issue with her ballot.
Lauren Cristella, president and CEO of the non-partisan group Committee of 70, says several errors can lead to a ballot being flagged.
"There are a few different ways that people can make a fatal flaw on their mail-in ballot. One of them is forgetting to sign it. Another is dating it incorrectly or not dating it at all," she said. "The other is to not use the secrecy envelope."
Officials in Philadelphia say they still have about 1,800 ballots with errors that need to be fixed.
The 6abc data team found Chester County has 388 ballots with errors. In Montgomery County, there were 240 as of Monday afternoon.
"I recommend everyone go to montcovotes.com to check the status of their ballots -- you can look it up. You just need your birthdate, your name, and your ZIP Code," said Montgomery County Commissioner and Board of Elections Chair Neil Makhija.
The Montgomery County Commissioner says voters who made mistakes still have time to cast a correct ballot.
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"You may want to go to the polls and the precinct and vote provisionally tomorrow (Tuesday) in case there's an issue," said Makhija.
"Go to an election office, you can request a new ballot," said Cristella, adding that the other ballot with an error would be canceled.
It's up to voters to find out if their ballot has any issues.
"We encourage everyone who voted by mail to go to the Department of State's tracker, www.pa.gov, then right in the middle of the page it says mail ballot tracked," said Cristella.
Voters hope to keep a ballot mistake from costing anyone their vote.
"I think it's really important that I make my voice heard and I hope others do too," Slavik.