American society rests on an assumption that families take care of their own. But 15 million Americans 50 and older didn’t have any close family — spouses, partners, or children — in 2015, the latest year for which reliable estimates are available. Most lived alone. By 2060, that number is expected to swell to 21 million. Beyond that, millions of seniors living on their own aren’t geographically close to adult children or other family members. Or they have difficult, strained relationships that keep them from asking for support.