A new U.S. Census Bureau report says the number of unmarried partners living together has tripled in the past two decades due to greater social acceptance.

The report released this week says the number went from nearly 6 million in 1996 to 19.1 million in 2018.

The report says unmarried partners are older, better educated, more likely to earn higher wages and more racially diverse than in the past.

Benjamin Gurrentz, a bureau survey statistician, writes that the growth in unmarried cohabitation reflects an increasing normalization. But it’s also viewed as an alternative to marriage for low-income and less educated people.

As a group, unmarried partners are still small compared with married partners, who numbered 127 million in 2018.

The report used data from the Current Population Survey.