. . . unmarried women are spectacularly loyal to the Democrats.

Yet unmarried women are spectacularly loyal to the Democrats.

And more from this The Economist article 

. . . unmarried women are one of America’s fastest-growing groups, leaping from 45m in 2000 to around 53m today—making them, in theory, a larger block of eligible voters than blacks and Hispanics put together (though in reality the groups overlap).

And in a related topic from an article in Demography (October 2013)

Results show that increases in the proportion of women unmarried by age 40 contributed most to the increase in childlessness in the late twentieth century, although these increases were offset somewhat by increased childbearing among unmarried women. The rising proportion of women with a college degree also explained a substantial amount of the increase in childless women.

The article is titled "Marriage (Still) Matters: The Contribution of Demographic Change to Trends in Childlessness in the United States," and it is by Sarah R. Hayford. 

Some illustrative graphs are here.