Many single people relish their autonomy and don’t necessarily want to be part of a couple (a 2005 Pew survey found that only 16 percent of unmarried people were looking for a partner). But some would like another option, a way to have companionship without entering into a romantic relationship.

That might mean roommate groupings that might be more stable than the 20-something variety. Ms. Bolick said one of her favorite living arrangements was the home she shared with a married couple. “I was living my own life, doing my own things, but had this kind of home base to return to,” she said.

Or it might mean a larger community that mixes shared and individual space. “Cohousing” communities around the country typically include private homes surrounding a common house where residents can gather for meals and other activities.

Joani Blank lives in a cohousing community in Oakland, Calif. Of 20 households there, she said, about 12 (including hers) are headed by single people. The community was founded 15 years ago, and 16 of its original members still live there. Residents prepare communal meals three times a week, and help one another in other ways; recently, one of Ms. Blank’s neighbors took care of her dog while she was away.