Fifty years ago, in 1968, living with an unmarried partner was rare. Only 0.1 percent of 18- to 24-year-olds and 0.2 percent of 25- to 34-year-olds lived with an unmarried partner, according to the Current Population Survey.

The measurement of cohabitation from 1968-1995 was less precise. The estimate came from an indirect measure of opposite-sex partners sharing living quarters, and the late 1960s through the early 1970s had particularly low reports of cohabitation.

Also, when comparing 2008 to 2018, years in which the Current Population Survey asked a direct cohabitation question, cohabitation only increased for 25- to 34-year-olds and slightly decreased for 18- to 24-year-olds.

So, although cohabitation has increased for young adults over the last 50 years, it is important to note the limitations in measurement and that certain periods of time did not produce increases in unmarried young adults living together.

In contrast to the rising rates of cohabitation, the proportion of young adults who are married has declined over time.

Today, 30 percent of young adults ages 18-34 are married, but 40 years ago, in 1978, 59 percent of young adults were married.