Marriage is also becoming stratified by economic class. Poorer Americans used to marry at the same rate as wealthy Americans, but that changed in 2008. Since then poorer Americans are significantly less likely to get married than their richer peers.
It's also interesting to see the fertility rate by income. Basically only bottom 20% and top 1% of US are above replacement rate. I can't find the graph I wanted to show this, but this one is pretty close: https://twitter.com/cschmert/status/993934031174725632
