According to a Gallup poll from this July, 45% of Americans say they have tried marijuana at least once in their lifetime. Taking into consideration the population of America, this means that 116 million Americans have tried the drug.
The poll used census data from last year to get this number which is significantly up from 1969. In that year, only 4% of Americans said they tried it. In 1999 the number was 34%.
The poll has also discovered that there was an increase in the people who used marijuana on a consistent basis. 12% of Americans said they use it regularly now compared to 7% four years ago.
The fact that more and more states are legalizing the drug medicinally and/or recreationally, there has been more opportunity for Americans to try it.