Marketing Challenge

Corporate America is figuring out ways to create products for, and market to, these multi-income, multifaceted families, Gallegos said.

Home builder KB Home is seeing increased demand for what it calls double master suites, two large bedrooms with attached bathrooms to accommodate parents living with their adult children, according to Cara Kane, a spokeswoman for the company, which is based in Los Angeles. All 10 of the largest communities in the U.S. ranked by their percentage of multigenerational households were within an hour's drive of the nation's second- largest city. All had populations over 100,000.

At the National Council of La Raza's National Latino Family Expo held in Washington, D.C., last month, businesses tried to reach as broad an audience as possible, according to Georgina Salguero, director of sponsorship for the event. Johnson & Johnson's booth featured everything from its namesake baby oil to Aveeno anti-aging creams. ConAgra Foods Inc. demonstrated modern takes on classic ethnic recipes, Salguero said.

Asian Impact

Asians, as well as Hispanics, are increasingly gathering under one roof. The state with the largest percentage of multigenerational households was Hawaii at 8.8 percent, twice the national average of 4.4 percent. The 50th state owes its large percentage to high real estate prices and the 47 percent of its population that is of Asian or Pacific Island descent, according to Sarah Yuan, a sociologist at the University of Hawaii at Manoa.

Her research on the state's Filipino residents found multigenerational households are most common among the poor, who live together so they can pool their resources, and the rich, who have the space.

"A lot of times it's for economic reasons," Yuan said in an interview. "Other times it's just cultural preferences."

Epicenter of Change

Few areas of the country have seen larger economic and cultural changes than Southern California. Norwalk, the Los Angeles suburb with the highest percentage of multigenerational households in the U.S., was mostly dairy farms in the 1930s. It was the hometown of former First Lady Patricia Nixon and the filming location for the 1946 noir classic "The Postman Always Rings Twice," about a bored, small-town wife who plots her husband's murder.

The city saw an explosion in residents after World War II as returning soldiers swelled the population to 35,000 in 1950 from 5,770 a decade earlier, according to a municipal history.