Since 2006, Hamilton firefighter Pat Hardewig has spent more than $100,000 on his hobby, though it only cost him about $20.

Hardewig is a “Georger,” one of more than 7 million users of Where’s George (www.wheresgeorge.com), a website that allows people to enter in the serial numbers of their money, mark them with the website address www.wheresgeorge.com, and then see where the bills travel, should someone notice the stamp and report its whereabouts.

“I’d seen the stamps on bills, and finally my curiosity got the best of me,” he said.

Since he tracked his first bill, he’s stamped more than 9,000 of all denominations and spent them as he normally would. More than 1,000 have been reported back in 47 states and four foreign countries, for a “hit rate” of about 11.74 percent.

“Personally, I’ve been to 37 states,” he said, “but my money has been to 47.”

The Where’s George website tracks all of this automatically, providing summary reports and travel reports for individual bills. Georgers are even given a “George Score,” created from a formula that factors in the number of bills entered, the number of hits received and periods of inactivity.

“A statistics freak would go nuts over this stuff,” said Hardewig, who has a George Score of around 1,010 and is ranked 104th in the state.

Georgers hope to get “Bingos” by getting a bill reported back from all of the counties in a state or all of the states. Hardewig lacks only Hawaii, Montana and Wyoming, and Delaware is the only state he’s hit a bingo by having hits on all three counties.

“One of my bills ended up in Hong Kong,” he said. “I’ve also had hits in Cancun and the Czech Republic.”

Since he started the hobby, he’s only found 31 more bills with a Where’s George stamp. He received one at the Cincinnati Oktoberfest that had been registered in Kuwait City, traveling more than 8,000 miles in six months.

Another Hamilton Georger, who goes by the name Buckeye Brian, has entered more than 18,000 bills into the Where’s George data base since 2007. He was working in Jacksonville, Fla., at the time, and withdrew a $20 bill with the stamp and became fascinated with the hobby.

“I have met Georgers from many parts of the country at gatherings,” he said. “At the gathering in St. Louis in 2011, I met people from all over the U.S. and a few from Canada.”

Where’s George rules prohibit the practice of “bill dumping.” Practices like depositing a large number of bills in the bank or paying for something at a store with a stack of $1 bills are prohibited and could get your account suspended.

But there are ways of increasing hits.

“One activity at gatherings is bill trading,” Buckeye Brian said. “One goal of many Georgers is to get hits in different states or counties, and trading bills helps them get hits in other counties. Bill trading involves envelopes with $10, which are usually 10 singles, but may be in other denominations.

“If I trade 10 singles with a person from Missouri, then I have a chance to get a hit in Missouri, and the other person has a chance to get a hit in Ohio,” he said. “Neither of us are allowed to hit the bill, but we may enter it in our favorites.”

Buckeye Brian’s George Score is currently floating around 1,100, with a hit rate of 12.77 percent. His bills have been hit in every state except Montana, and he has also had bills hit in Iraq.

Going on vacation is also a good way to accumulate out-of-state hits.

“I usually get a stack of 50, $1 bills when we go on vacation,” Hardewig said, who is also an anime aficionado and goes to a lot of conventions and gatherings for that as well as firefighter training and conferences. “I took a stack down to Hilton Head, but very few of those bills surfaced again.

But mostly it’s “catch and release,” he said.

While the Where’s George hobby takes a fair amount of time to enter the bills, our Hamilton Georgers are not as fanatic about it as others. Buckeye Brian has met some of the top Georgers in the country, some who have entered more than 2 million bills.

There are nearly 250 million bills entered into the Where’s George database, according to the website. Or about 0.111 percent of all U.S. currency in circulation. The national hit ratio is 11.67 percent.

Where’s George was founded in 1998 by Massachusetts data base consultant Hank Eskin.

“I was going to lunch one day and had a dollar bill in my hand that had a message written around the border: ‘Write this message on 10 other bills and good luck will come to you,’ ” Eskin said in a “Where’s George” documentary on Youtube.

“I thought this was interesting,” he said. “How did this get on the bill? How did it get to me? Where is it going to go next.”

When he learned that each dollar bill has a unique serial number that allows it to be tracked like a UPS package, he created the website and watched it grow.

While Where’s George was designed to be nothing more than an interesting hobby, the site data has been used for statistical analysis of human travel and was used to predict the pattern of influenza outbreak in a Northwestern University study during the 2009 swine flu outbreak.