As marriage rates have fallen, the number of U.S. adults in cohabiting relationships has continued to climb, reaching about 18 million in 2016. This is up 29% since 2007, when 14 million adults were cohabiting, according to U.S. Census Bureau data.

Roughly half of cohabiters – those living with an unmarried partner – are younger than 35. But an increasing number of Americans ages 50 and older are in cohabiting relationships, according to a new Pew Research Center analysis of the Current Population Survey. In fact, cohabiters ages 50 and older represented about a quarter (23%) of all cohabiting adults in 2016.

Since 2007, the number of cohabiting adults ages 50 and older grew by 75%. This increase is faster than that of other age groups during this time period and is driven in part by the aging of Baby Boomers. In 2016, 4 million adults ages 50 and older were cohabiting – up from 2.3 million in 2007. By comparison, 8.9 million adults ages 18 to 34 were cohabiting last year, up from 7.2 million.

While cohabitation is rising, cohabiters still make up relatively small portions of each age group – particularly among adults ages 50 and older. In total, 7% of U.S. adults were cohabiting in 2016. Just 4% of adults 50 and older were cohabiting. By comparison, 14% of Americans ages 25 to 34 were cohabiting – the highest share among the age groups analyzed here. Roughly one-in-ten adults ages 18 to 24 and 35 to 49 were cohabiting.

The rising number of cohabiters ages 50 and older coincides with rising divorce rates among this group. With the higher divorce rates and a growing share of people who have never been married in this age group, more individuals are unmarried and available for partnering or re-partnering. In 2016, 61% of adults ages 50 and older were married, compared with 64% in 1990.

Most cohabiters ages 50 and older have previously been married, including a majority who are divorced (55%). Just over a tenth of cohabiters ages 50 and older (13%) are widowed – a share that rises to 27% among cohabiters 65 and older. Still, about one-fourth of cohabiters (27%) ages 50 and older have never been married.

By contrast, majorities of cohabiters younger than 50 have never been married, including nearly all cohabiters ages 18 to 24 (97%) and 85% of those 25 to 34. About half (52%) of cohabiters ages 35 to 49 have never been married, while roughly a third (36%) are divorced.

Among cohabiters ages 50 and older, a majority (57%) are in their 50s. Another three-in-ten are in their 60s, while one-in-ten are in their 70s. Just 3% of cohabiters ages 50 and older are in their 80s or older.