THE NUMBER OF AMERICAN NEWBORNS with hyphenated surnames is in decline. Oddly enough, the Census Bureau hasn't kept count: their computer records automatically change Smith-Jones into Smithjones. But judging from the reports of birth registrars around the country and lots of first-person narratives, it appears that surname hyphenization peaked in the late 1980s / early 1990s.
As a general but not ironclad rule, hyphenizer parents were either college-educated pro-feminist couples or single/divorced mothers who wanted their kids to have their name as well as the name of their absent fathers. The overall number of people who fit in those two categories has continued to increase relative to the general population, but the number of new hyphenated baby surnames is sharply down. Among the reasons given: record-keeping confusions; the problem of exponential surname growth as hyphenated persons sire children with other hyphenated persons; a general tendency for a new generation of feminists to distinguish itself from the pioneer cohort of the 1970s.
As a recidivist procreator, I have a personal angle on the hyphen craze. In 1977, when my first wife was pregnant with our first child, we had to decide on a last name. My wife thought hyphenization made sense. I didn't like the hyphen for a number of reasons. It was, historically, an anglophile affectation (Simon Babbington-Smythe, Basil Fornsby-Trotwood), and I always tried to be conspicuously Irish. The potential for awkward complications in second and third generations was pretty obvious. And, in general, the custom of hyphenating the surnames of offspring to advertise a family's commitment to equality was too identified with a social and political class to which I belonged but with whom I didn't want to identify. So my wife and I made a deal. We agreed to follow what we thought would be a growing trend: give a baby boy his father's surname and a baby girl her mother's. Hence Benjamin Nugent, born 1977, and Annie Baker, born 1981. The growing trend turned out to be nothing of the kind, of course, and so when NugeFam 2.0 was launched in 1999, all the kids, both sexes, got dad's moniker. No big deal. And you have to admit that Annie Baker is a great name.