Goodwill employee Lakeisha Williams was sorting through some donated books at a Stockton, Calif., collection site when she noticed an unexpected donation.

"There was an envelope full of cash," Williams told ABC News' Sacramento affiliate KXTV.

The envelope had $10,500 in it in $100 bills. Williams joked that she briefly thought about pocketing the cash but knew she had to do the right thing.

Lakeisha Williams found an envelope full of cash among some donated books. (Photo credit: ABC News)

"My concern was somebody was out that money, and I would have liked for them to get it back," she said.

She handed the cash over to a manager about a month ago, and the money had still not been claimed.

Goodwill Industries of San Joaquin Valley President David Miller said that it had not gone unnoticed that Williams "kindly and correctly" returned the money.

"What we did is we take the money … and put it into a holding account, and we wait usually a pretty good amount of time to see if somebody comes forward and identifies themselves and says they made a donation and a mistake," Miller told ABCNews.com today.

Authorities were contacted in case anyone reported money missing, and the money will be held in the bank account for "no less than 120 days," he said.

"If nothing happens at that point … and all indicators are that nobody is claiming the money, at that point in time we put it into our normal donation stream revenue for our agency," Miller said. "We have a policy to reward our employees for their honesty and integrity. …"

The amount of money rewarded to the employee is up to Miller, but he said it would likely be in the range of 10 percent in this instance. This means Williams could be about $1,000 richer if no one comes forward to claim the missing money in the next three months.