"I looked through the full 2010 The State of Our Unions report. This graph, showing the percent of those aged 15 or older who were married from 1960-2009, shows that marriage has become less common for both men and women, Blacks and Whites (based on U.S. Census Data).
Of course, this is in large part because people in the U.S. are getting married later; not only do we not really expect a 15-year-old to be married, we’d be rather horrified if they were. If we look only at adults aged 35-44, we do see a significant decrease in marriage between 1960 and 2009, but still, about 2/3 were married":
Found at Sociological Images, where there are also graphs regarding divorce and cohabitation.