The National Center for Family and Marriage Research at Bowling Green State University has issued a report entitled "Young Adults in the Parental Home, 1940-2010" (link). The report uses U.S. Census data, primarily, to plot living-at-home percentages by gender, age (18-24 vs. 25-34), and marital status. In general, young adults living in their parents' house was quite common in 1940, declined until 1960, and then showed very gradual increases over the next 50 years.
Interestingly, the percentages of single male and female 18-24 year-olds living in their parents' home as of the most recent data (54% and 50%, respectively) are lower than in 1980, although there was a slight uptick from 2000-2010. For 18-24 year-old married adults, in contrast, there has been a dramatic rise in co-residence with parents from 1980 (6% of men, 5% of women) to 2010 (21% and 20%, respectively).
