This raises a fascinating question, since the U.S. appears still to be on the trailing edge of change. Taking Sweden as the "leader", if you'll pardon the expression, the US is at 38% less, 21% less than France, and 17% less than Britain.
But this is deceptive, because some demographic groups tend to breed more bastards than others and a different breakdown might be more useful.
In other words, the U.S. may be in much better shape than it appears, or worse, depending on your point of view.
Swedes are less inclined to marry in the traditional sense but more inclined to long-term shack-up arrangements (or common law marriages). If people live together for life without officially marrying and raise children that way, then it would be hard for me to deny it's a viable family.