As the ranks of senior citizens grow and younger Americans continue to postpone life milestones that previous generations achieved earlier in life, more than a quarter of American households are made up of people living alone.

According to the U.S. Census Bureau, there will be 37 million one-person households in the United States in 2021, accounting for 28 percent of all households and 15 percent of the total population.

In 1960, only 13% of households were occupied by a single person. The number of Americans living alone has increased by 4 million in the last decade.

Only half of American adults, or 50%, live with a spouse, down from 52% a decade ago. At the same time, the proportion of Americans who live with an unmarried partner is increasing – today, 8 percent of Americans over the age of 18 live with a partner to whom they are not wedded, almost double the 4.1 percent rate the Census Bureau measured in 2001.

These two figures reflect a long-term trend in which Americans postpone marriage until later in life. When the Census Bureau first examined marriage data in 1947, the median man was 23.7 years old, and the median woman was 20.5 years old.

Today, the median age of a man when he first marries is 30.4 years, while the median age of a woman is 28.6 years. Today, 34% of all Americans over the age of 15 have never married, compared to 23% in 1950.

The data are manifestations of a population that makes critical life decisions at later ages than previous generations at the same age. The evidence is most visible in birth rates, which have been steadily declining for decades – and more precipitously in recent years, a phenomenon known as the Baby Bust by demographers.

“More young adults living alone, as well as an increasing age at first marriage, are both likely to reduce the number of births. Of course, not all births result from marriage, but the rise in young adults living together and postponed marriage reflects shifting societal attitudes toward families and children “Kenneth Johnson, senior demographer at the Carsey School of Public Policy at the University of New Hampshire, agreed.

According to the National Center for Health Statistics at the Centers for Disease Control and Prevention, the number of American women who gave birth in 2020, a year in which many decisions to have or grow a family may have been influenced in part by the pandemic, fell at the steepest rate since 1973. According to Johnson, the drop occurred despite the fact that there are more women of child-bearing age in the population than a decade ago.

Birth rates were lower in every month of 2020 – including January and February, before the pandemic imposed lockdowns, and subsequent months, when pregnancies began long before the coronavirus dominated news headlines – compared to 2019.

The trend has continued this year, with births falling another 5% in the first three months of 2021 compared to the already-record low of 2020.

In 2020, there were slightly more than 3.6 million births, about 700,000 fewer than in 2007, when American births peaked.

The intervening years included the Great Recession, which left the Millennial generation far behind their forefathers in areas such as savings, debt, and accumulated wealth – all of which tend to be precursors to decisions about whether to buy a home, marry, or start a family.

Johnson, a fertility expert, estimates that the fertility declines that began during the Great Recession have resulted in approximately 7.6 million fewer births than would have been expected over the same number of years at a previous point in American history.

Another sign of postponed life decisions is the growing number of young people living with their parents. According to the 2021 figures, 11.2 percent of adults over the age of 18 still live with their parents, up from 10% in 2001 and 10.6% in 2011.