What is the most commonly counterfeited bill in the United States?
According to the Secret Service Agency, the most commonly counterfeited denomination in the United States is the $20 bill. By contrast, the $100 bill is the most counterfeited note outside of the US. Lately, however, even small bills such as $1 and $5 notes have been seen in low-income neighborhoods, such as the Florence-Firestone section of South Los Angeles. "It's gotten to the point where they are counterfeiting the ones and the fives," said Efren Martinez of the Florence-Firestone Chamber of Commerce. "Normally business owners don't check those."
SOURCE: Fake Money A Growing Problem For Small Businesses | Los Angeles Times