Americans are older than ever before, with a median age of 35.3 - two years older than a decade ago. The number of people over age 85 has increased at a faster rate than almost any other segment of the population, to 4.2 million.

Women are more independent, heading up more households and rearing more children on their own. And the number of people living together as unmarried couples, both straight and gay, has skyrocketed by 72 percent.

This is the new America, according to the latest information released from the 2000 Census, a nation where the term ''family'' has changed dramatically in the last 30 years, and where a greater number of people live in isolation.

More than 27 million people, nearly 10 percent of the American population, live alone, a rise of 21 percent over the past decade. Though the census data do not indicate this directly, demographers believe that a sizable portion of people living alone are senior citizens.

Behind the rising median age lie several broad trends. The country's birth rate has slowed slightly, and the number of seniors has increased as Americans live longer. And the number of middle-aged Americans has swelled as the baby boom generation, those born between 1946 and 1964, grows older, leading to a 49 percent jump in those between the ages of 45 and 54. Meanwhile, there were actually fewer Americans between age 20 and 35 than in 1990.

Demographers expect to see the numbers of Americans over age 65 start to balloon in the next few decades, but note that widespread concerns about a disproportionate ratio of retirees to workers may be overblown.

Because of increased immigration, the ratio of workers to elderly people will actually grow, said Barry Edmonston, director of the Population Research Center at Portland State University. In 20 to 30 years, Edmonston said, America will have ''the lowest number of retired people to workers.''

Besides the country's age, some of the most striking changes have been in the number of households headed by women, both with and without children.

The number of single mothers with children has jumped 25 percent, and now represents more than one in five households with children.

Meanwhile, the number of traditional families - defined as a married couple with at least one child - has increased much more slowly, growing at only half the rate of the overall number of households.

Overall, nearly 13 million women now head households - a rise of 2.2 million during the 1990s.

''The women's liberation movement of the '70s was accelerated by the change in economy, in which women needed to work,'' said Carl Haub, a demographer with the Population Reference Bureau, a nonprofit research group. ''So right then and there the ground was laid for women.''

He said two trends have caused the rise of women as heads of households: Career-oriented women are delaying marriage, and many are chosing to live on their own. He said it is far more accepted today for women to be single mothers than in the past.

The rise in single motherhood is closing the gap between American women and those of many European countries. In Sweden, more than half of the births in 1999 were to unmarried mothers. In Iceland, it was 62 percent. In France, it was 40 percent in 1997.

In America, Haub said, a disproportionate number of minority women give birth out of wedlock. Sixty-nine percent of the black babies born last year were to single mothers, compared to 42 percent of Latino births and 22 percent of white births. (There were no data on Asians or Native Americans.)

As the social obstacles to single motherhood have fallen, the same is true for unmarried couples, whose numbers have grown dramatically in the past 10 years.