CDC's Vital Signs: Adult Smoking in the US
"Tobacco use remains the single largest preventable cause of disease, disability, and death in the US. Some people who smoke every day are smoking fewer cigarettes; however, even occasional smoking causes harm. The percentage of American adults who smoke decreased from 20.9% in 2005 to 19.3% in 2010. That translates to 3 million fewer smokers than there would have been with no decline. But almost 1 in 5 adults still smoke..."