Married couples make up fewer than half of the households in Tennessee, Hamilton County and Georgia and barely a third of the households in Chattanooga.
Recently released 2010 census data shows 46 percent of Hamilton County households contain married partners, compared to 50 percent in 2000. Statewide figures for Georgia and Tennessee also slipped below 50 percent for the first time, to 48 and 49 percent, respectively.
Many factors, from life expectancy to attitudes and even the recession, could be leading to the decline, according to demographics expert Doug Bachtel.
"It's expensive to get married, and as a result people could be actually delaying the ceremony," said Bachtel, a demographer with the University of Georgia. "That might be a line the guys are using."
The percentage of married households was higher across the region, with Walker, Catoosa, Whitfield, Marion and Bradley counties all in the 53 to 56 percent range.
But even those counties saw noticeable drops from the 2000 census, when most of their figures were around 60 percent.
Carol Kutchins, who runs The Marriage Consultant on Broad Street, said the figures are "a sign of the times."
She compared modern society to life in the book and the television series "Little House on the Prairie," in which groups of people needed traditional family units to survive.
"There's a big difference between now and then, where I can say, 'No, I don't like you,' and go get an apartment," she said.
The numbers in Chattanooga, Nashville and other urban areas are even lower than the state figures, which doesn't surprise Bachtel.
"A lot of people feel like if you are living together with somebody without marriage, you're living in sin," he said. "It's rather easier to live in sin in a city."
In the bigger picture, Bachtel believes, age and attitudes may have a lot more to do with the trends than a short-term factor such as a down economy.
He said the population of Georgia in particular skews young, and because of that there are probably more unmarried residents than in states with older populations.
"We're at that young population; they may not be ready to get married," he said.
The Census Bureau also accounts for other relationships within the household. The data for Hamilton County shows 29 percent of households are people living alone, 6 percent include relatives who are not children, 5 percent include nonrelatives and 2.9 percent are group quarters. The data does not include a line for same-sex couples because such unions are not officially recognized.
But experts such as Bachtel also have noted the declining marriage rate since the 1960s, which he said is due to changing attitudes.
"A lot of people feel they can live together and just try it out for a while," he said.
The number of heads of household living with unmarried partners increased in both states and most area counties from around 1.5 percent in 2000 to 2.2 or 2.3 percent in 2010, according to census data.
Kutchins sees those statistics in action frequently.
"I don't think we're seeing marriage as the same way we used to," she said. "People are seeing couplehood in a lot of different ways."
But Julie Baumgardner, executive director of First Things First in Chattanooga, said that can be dangerous. She cited statistics indicating that couples who live together before marriage are less likely to be happy once they tie the knot.
"There's no commitment," she said. "There's a sliding [into marriage] versus a deciding."
Baumgardner said statistics can be misleading. A widow who was happily married for 50 years before her husband died would be considered unmarried in the census count, she pointed out.
"There are lots of variables that are involved in that number," she said. "Clearly, people are still marrying."
And some of those variables come with dollar signs.
For women on government assistance, marriage actually can hurt their ability to qualify for some programs, Baumgardner said.
Kutchins said people also are paying more attention to the legal and financial sides of marriage, especially in second and third marriages. She has noticed divorcees staying unmarried longer in recent years and has talked with many couples who are cautious about sharing and potentially dividing their finances.
"People have learned that it's a legal transaction, not just a love transaction," Kutchins said.
As to what the trend means, experts are unsure.
Kutchins said she sees people continuing down the "road of confusion" and said the culture needs to do a better job of preparing young people for long-term relationships.
"It discourages me, because it tells me there are a lot of people who are discouraged," she said.
Tom Buchanan, an associate professor of sociology at the University of Tennessee at Chattanooga, said the jury is still out.
"There are a lot of debates about the family," he said. "The thing that it doesn't equate to is, are there terrible consequences? You can't make that leap."