In any U.S. city, living arrangements run the gamut from friends and strangers living as roommates to domestic partnerships to single-parent households to the traditional nuclear families. While the vast majority of Americans cohabitate in one way or another, there are also those who live alone – either by choice or by circumstance.

Across the United States, about 1 in every 10 Americans – 10.3 percent – live alone. More than 1 in every 4 households – 27.9 percent – are made up of a single individual.

In some cities, however, living alone is far more common. According to estimates from the U.S. Census Bureau, there are 21 metropolitan areas where more than one in every three homes are occupied by individuals who live alone. While these cities do not necessarily share a single defining quality, there are some common characteristics that may help explain why residents are more likely to live on their own in these places.

Living alone means footing the bill for utilities and rent – or upkeep and mortgage. For that reason, it is not financially prudent, or even possible, for many. In cities with a lower than average cost of living, fewer residents may need to rely on a roommate in order to afford housing.

The Barnstable Town, Massachusetts metropolitan area, which comprises Cape Cod, is the only metro area where the most people live alone that has a higher than average cost of living. In the remaining cities where the most people live alone, goods and services are as much as 17% less expensive than they are on average nationwide.

Not surprisingly, the cities with the most one-person households also tend to have large single populations. Nationwide, 48.1 percent of the 15 and older population are currently married. In the majority of cities with the largest share of people living alone, a smaller than average share of the population is married.

Just as there are those for whom living alone is a choice, there are also those who are living alone due to circumstances outside of their control. Often, this means the passing of a spouse or family member. In 14 of the 21 cities where the most people live alone, a larger share of the 15 and older population is widowed than the 5.9 percent national share.

Many people live alone following the death of a spouse, particularly those older Americans who are less likely to remarry. The cities where more people are likely to live alone tend to have older populations compared to the U.S.

Regardless of marital status or age, households in every city on this list are less likely than most to have children. In the cities with the most people living alone, the share of households with at least one resident 18 or younger ranges from 28.7 percent in Macon, Georgia, to 17.6 percent in Barnstable Town. To compare, 30.8 percent of households nationwide are home to at least one child.