The United States as a whole has witnessed a decline in its Family Structure Index score in recent years. By definition, the U.S. had an FSI score of 100 in the year 2000, with 64% of prime-age adults married, 68% of teens in married-parent families, and a total fertility rate of 2.05 children per woman.

In 2010, the U.S. had an FSI Score of 92.8, a 7.2% decline from the turn of the millennium. As of 2024, the U.S. FSI score has fallen to 87.3.

The 2026 Family Structure Index (FSI) tracks the health of the family by measuring three variables: the share of adults ages 25 to 54 who are married, the share of teens living with married parents, and the total fertility rate. As we look across the last decade, we have bad news and good news to convey in this report. The bad news is that marriage and fertility have fallen in most states across the nation in the last ten years. The good news is that the share of kids being raised in married families across America has leveled off.

From 2000 to 2010, these declines were largely driven by falling marriage rates in the U.S. In this time period, the share of adults 25 to 54 who were married fell from 64% to 57%, an 11% decline. By contrast, the share of teens living in married parent families fell by 6%, and the score for the total fertility rate fell by 4%.

From 2010 to 2024, the total fertility rate had the greatest impact on the national Family Structure Index, falling by 17% over this time period. Declines in the share of prime-age adults married largely flattened after 2015, along with the share of teens in married-parent homes. The total fertility rate in America continues to fall.

South Carolina has risen the most in the Family Structure Index over the past 10 years, moving from 45th in 2014 to 28th in 2024, the latest year with available data. This is in large part due to a rising share of prime-age adults who are married in South Carolina. In 2014, 52.6% of South Carolinians ages 25 to 54 were married. That rose to 55.1% by 2024, an increase of 4.7%.

Hawaii, on the other hand, saw the largest declines in marriage over this time period. In 2014, 56.1% of Hawaiians ages 25 to 54 were married. This fell to 52.1% by 2024, a 7.1% decline.

In South Carolina, the share of teens in married parent homes, a high correlate with prime-age marriage, is also on the rise. Still, the South Carolina share is below national averages. The latest data show that just 59% of South Carolinian teens live in a married parent home, compared to the national average of 63%. But this gap is shrinking as marriage gains ground in the Palmetto state. And while the total fertility rate has fallen substantially, South Carolina is now above average compared to U.S. as a whole when it comes to fertility.

South Carolina, being 45th in the nation in 2014, has had a lot of room to grow. We are witnessing the increased fortunes of South Carolina as it has risen 17 places in the past 10 years. Hawaii, by contrast, has fallen a staggering 16 places, from 10th to 26th, nearly at parity with South Carolina (28). Whereas Hawaii excelled in the nation for teens in intact families, it is now roughly equivalent with national averages, and is lower than the nation on the share of prime-age adults married.

South Carolina and Hawaii represent the two extremes of state trends. While declining total fertility rates have been driving national declines in the Family Structure Index, marriage trends are behind recent shakeups in state rankings. Most states in the union saw some declines in their prime-age married population, with larger declines on the West Coast, New England, and the Great Lakes region. Among the seven states that saw increases over this ten-year period, South Carolina, Florida, and Mississippi witnessed the largest.

One big reason that marriage is rising in these states is that red states are attracting more families. Migration patterns, where families with children are moving in greater numbers from blue states to red states, explain a significant portion of the changing fortunes of marriage in these states. We compared the net domestic migration rate for each state to the change in the share of prime-age adults who were married. We found that domestic migration rates accounted for 30% of the variance between states over this time period. More domestic inmigration is associated with boosts in the share of prime-age population who are married. Domestic outmigration, prominently seen in New York, Alaska, Illinois, and Hawaii, is associated with a declining share of prime-age adults being married.

We calculated the Family Structure Index of Red and Blue America using state votes from the 2024 presidential election, from 2010 to 2024. We found that the gap between Americans in Blue and Red states has widened substantially since 2019.

Blue state Americans have higher shares of children in married-parent families, largely because they are better educated, whereas Red state Americans have more prime-age adults who are married and higher birth rates. And while Red state Americans are slowly closing the gap on married parent families with Blue state Americans, the driver of the widening Family Structure Index gap is marriage among prime-age adults. Looking over the five-year period of 2019 to 2024, Americans from Red states saw increases in the share of prime-age adults married (+1.8%) and the share of teens in married-parent families (+0.2%). More generally, over this time period, Red states witnessed an increase of 600,000 children, driven both by migration from Blue states and a relatively higher fertility rate. Notably, Blue states also saw declines in their total population of children, having 600,000 fewer children in 2024 than in 2019. This is driven both by falling childbearing and by rising outmigration to Red states. While both Red and Blue states saw declines in their respective total fertility rates, Blue states took a harder hit.

Two variables go far in explaining state-level fertility. Using Pew’s 2023–2024 Religious Landscape Study, we were able to compare average religious attendance by state with state-level total fertility rates. We found that states that have more religious adults tend to have higher fertility rates. Fitting a polynomial regression, frequent religious attendance (once or more a week) explains 57% of the variance in total fertility rates between states.

Northeastern states like Vermont, New Hampshire, and Massachusetts have less than 15% of their adult population frequently attending religious services and have fertility rates at or below 1.4. By contrast, states like South Dakota, Utah, and Mississippi have at least 40% of their adult population frequently attending religious services and have total fertility rates at or above 1.8. The family-first cultural orientation of American churches helps explain this association between faith and family life when it comes to fertility.

Birth rates vary by state according to housing prices, as well. We examined the typically priced 2-bedroom home (single-family, condominium, and co-ops) for each state and divided this dollar amount by the median income of adults ages 25 to 54 working full-time. This gave us a price-to-income ratio, which we compared to the state-level total fertility rate. Expensive 2-bedroom housing explained 25% of the variance in total fertility rates between states. California and Hawaii were outliers in expensive housing, with typical 2-bedroom homes costing 9.5 and 10.4 times the median salary for prime-age adults, respectively. Excluding California and Hawaii, expensive housing explains 31% of the variance between states.

South Dakota, Utah, and Idaho stand notably above the model line, and Vermont below. Indeed, one reason that red states tend to do better on the FSI is that often offer more affordable homes to ordinary American families. This is a major reason that the nation has seen what family scholars Lyman Stone and Brad Wilcox call a “ Blue State Family Exodus.”

States that have a greater share of adults with a college education tend to have more teens living in married parent families. This is in keeping what the family scholars Naomi Cahn and June Carbone have argued in the sense that a college education gives parents a better shot at securing higher paying and more stable jobs. Such jobs, in turn, provide families with a secure financial foundation that minimizes the stresses that can destabilize family life. The point here is that one reason states like New Jersey, Minnesota, and Washington score high on this measure of family instability is that they tend to have more educated parents who are employed in stable and good paying jobs.

Conclusion

There is good news and bad news to report when it comes to making sense of the State of Our Unions in America. The bad news is that family formation has continued to fall since 2014 across the nation, as measured by ongoing declines in the fertility rate. The good news is that the downward trend in marriage-related trends for adults and children have leveled off in recent years. Currently, 57% of prime-aged adults (25-54) and 63% of teens are living with married parent across the United States.

The question is whether states can make moves to push these marriage and family trends in a better direction. In recent years, some Red states have improved on the Family Structure Index, partly because they have succeeded in appealing to married Americans, including married families, who are leaving Blue states for them. More affordable homes, stronger job growth, less taxes, a greater emphasis on law and order, and a more pro-family culture are the kinds of factors that have made Red states relatively more appealing to married families with children along with young marrieds aiming to start a family. At the same time, states like New Jersey and Maryland have seen their family fortunes improve as they attract more college-educated families with strong economic growth.

The lesson going forward is clear: red and blue states alike should advance public policies that make single-family homes affordable, jobs plentiful, taxes low, and good educational options abundant — all while fostering communities where families can thrive. Given the deep connections between strong families and the American Dream, doing so will put that Dream within closer reach of the men, women, and children across their states.