A record low of barely half of Americans are currently married, according to a Pew Research Centre analysis of Census data, reports the BBC.
Just 51% of adult Americans are married, compared with 72% in 1960.
The median age of first marriage has also hit a new high, of 26.5 for brides and 28.7 for grooms.
Pew said the number of adults co-habitating, single-person households and single parents had meanwhile increased in recent decades.
The study found that 20% of adults today aged 18 to 29 are married, compared with 59% in 1960.
It is unclear whether they are delaying matrimony or abandoning it altogether.
While Pew did not study reasons for the trend, it noted that the marriage rate for college-educated adults declined "far less" than among the less-educated.