According to IT security company Sophos, the largest share of spam mail worldwide originates in the United States.
24.2 percent of all junk mail comes from the US, miles ahead of any other nation. France is a very distant second with 6.7 percent while China rounds off the top three with 6.2 percent. Why is the US responsible for such a massive portion of the world's spam? Its large population and considerable share of the world's internet infrastructure seem to be the primary reasons.
This chart shows the percent of all spam in Q2 2014 originating in each country.
You will find more statistics at Statista