More Americans are living alone than ever before, according to a new U.S. Census Bureau report that looks at how families and living arrangements have changed over time. In 1970, only 17 percent of the U.S. population was living alone. By 2012, the proportion of single-person households increased more than 10 percentage points, to 27.4 percent. The share of households that were married couples with children has halved since 1970, from 40 percent to 20 percent, according to the report.