In the small town of Hinsdale, New Hampshire, people knew Geoffrey Holt as the unassuming caretaker of the mobile home park where he lived.

What they didn't know was that he was a multimillionaire — and he donated the entirety of his $3.8 million fortune to the 4,000-person community after he died at age 82 in June.

When Holt suffered a stroke in September 2021, his best friend and one-time employer Edwin "Smokey" Smith became his primary caretaker and estate executor, according to the Brattleboro Reformer.

"Geoff was a private person, preferring to be in the crowd rather than in the front of it," Smith tells CNBC Make It.

Holt had previously confided to Smith about his wealth, but Smith didn't know of Holt's plans until he became caretaker.

"I wasn't particularly surprised," says Smith. "Except I expected him to leave his money with more than one place."

Holt's fortune was placed in the care of the New Hampshire Charitable Foundation.

Grants will be made "to honor Mr. Holt's wishes: support projects, programs and organizations that provide health, educational, recreational or cultural benefits to the residents of Hinsdale," an NHCF spokesperson tells CNBC Make It.

A shrewd investor, Holt invested in several mutual funds that grew over the years. "He was quite surprised that his investments had done as well as they did," says Smith.

Holt settled in Hinsdale in the 1970s after serving in the Navy. He didn't own a car and lived frugally in a mobile home on the 25-acre land Smith owned.

"It was his oasis in the world," says Smith. "He could remove himself from everyday life, read and enjoy nature, the views, a brook, birds and all else that goes with his private hideaway."

The same thing happened in a town 7 miles away

Interestingly, this isn't the first time a secret millionaire in the area has made a sizable donation to their hometown.

In 2014, janitor and gas station attendant Ronald Read passed away at age 92 in Brattleboro, Vermont — right across the state border from where Geoffrey Holt lived in New Hampshire.

Like Holt, Read had quietly amassed wealth through shrewd investing and frugal living over the years, unknown to even his closest friends. When he died, he bequeathed $6 million of his $8 million fortune to Brattleboro's local hospital and library.

In Read's case, he typically invested in blue-chip stocks that paid dividends. He would then use those dividends to invest in more stocks, according to The Wall Street Journal.

Asked if Read inspired Holt, Smith says he doesn't think so, because Holt never mentioned it. However, the story was reported in newspapers that Holt regularly read, so it's possible that he was at least aware of Read's generosity.

As for Read, his $4.8 million to Brattleboro Memorial Hospital had personal significance, as he was a regular at the hospital's cafe.

"He always had a cup of coffee and an English muffin with peanut butter," a friend said shortly after he died. "That was it. And he always sat at the exact same stool at the counter."

DON'T MISS: Want to be smarter and more successful with your money, work & life? Sign up for our new newsletter!

Get CNBC's free Warren Buffett Guide to Investing, which distills the billionaire's No. 1 best piece of advice for regular investors, do's and don'ts, and three key investing principles into a clear and simple guidebook.