Pew Research Center

According to a Pew Research Center poll on attitudes toward premarital sex 38 percent of adults in the US think that premarital sex is always or almost always wrong (note that the question is framed in terms of heterosexual couples only).

I thought this was odd given that a much smaller percentage of people actually do wait until they are married before having sex, so I poked around in some of the charts. In terms of basic demographics, there are predictable differences between people's attitudes depending on their age group, with older respondents being more likely than younger ones to think that premarital sex is wrong. Other demographic factors that are correlated with a greater likelihood of thinking premarital sex is wrong include income (as income goes up tolerance for premarital sex also goes up) and education (people with more education are less likely to think that premarital sex is wrong), thought the differences are small.