The idea behind setting aside the third week in September to honor singles and unmarried people began in Ohio in the 1980s, the Census Bureau said in a release on statistics based on 2011.
Of the unmarried U.S. adult residents, 53 percent were women and 47 percent were men, data indicated.
The percentage of unmarried U.S. adults who had never been married is 62 percent, while 24 percent were divorced and 14 percent were widowed, the Census Bureau said.
The bureau said there were 89 unmarried men for every 100 unmarried women in the United States and that 55 million households were maintained by unmarried men, about 46 percent of households nationwide.
In households with children, 13.6 million unmarried parents were in such living arrangements. Of this total, 10.0 million were unmarried mothers, 1.7 million were unmarried fathers and 1.9 million were unmarried couples with at least one shared child.
The number of people who lived alone in 2011 was 33 million, 28 percent of all households, the Census Bureau said.
The bureau said there were 6.8 million households with unmarried partners. Of that total, 593,000 were same-sex households.