Some 47 million Americans 5 and older used a language other than English in 2000, the bureau said. That translates into the nearly one in five, compared with roughly one in seven 10 years earlier.
There also were more people considered "linguistically isolated" because of limited English, a situation that some analysts say can prevent people from assimilating fully into American society and hinder activities like grocery shopping or communicating with police or fire officials.
The Spanish-speaking population rose by 62 percent over the period to 28.1 million; slightly more than half also reported speaking English "very well."
The numbers are a further reflection of the surge in immigration since 1990. The influx helped make Hispanics the largest minority group, surpassing blacks.
California, New Mexico and Texas had the highest percentages of residents who did not speak English at home, but the greatest increase during the decade occurred in states that experienced explosive Hispanic immigration: Nevada, Georgia and North Carolina.
The trend has had vast ripple effects across American culture.
Many school districts are scrambling to find bilingual instructors to teach an influx of immigrant students. America Online launched its "AOL Latino" service last week targeting homes where Spanish is mostly or exclusively spoken.
For the first time, the Census Bureau printed out questionnaires in 2000 in languages other than English: Spanish, Chinese, Tagalog (the main native language of the Philippines), Vietnamese and Korean.
Marisa Demeo, regional counsel for the Mexican American Legal Defense and Educational Fund in Washington, said governments have a legal obligation to help those who don't speak English well.
Such obligations, she said, "have been there for a long time. It's just that the demand hasn't been as great as it has been the last few years."
More companies are diversifying advertising or marketing campaigns to reach people who speak other languages, said Saul Gitlin, an executive vice president at Kang & Lee Advertising in New York, which specializes in Asian-American multicultural communications.
Data in the census report come from responses to the 2000 census long form survey distributed to about 1 in 6 households. The question asked if a person spoke a language other than English at home, and if so, it then asked to gauge how well they spoke English.
The proportion of the population 5 and older in 2000 who spoke English less than "very well" was 8 percent, up from 6 percent in 1990 and 5 percent in 1980.
The bureau found about 11.9 million people lived in linguistically isolated homes, meaning nobody in the home 14 or older knew English "very well." That was up 54 percent from 1990.
The category is used in part to gauge how well people who speak another language can communicate in English in common activities like speaking with police or doctors, or at the bank or grocery store.
In particular, Hispanics often live in neighborhoods where most people tend to speak a language other than English, said John Logan, a sociologist at the State University of New York at Albany, who has conducted research on the issue. He said that level of isolation can lead to a continued reliance on Spanish, even among those born in the United States.
Groups like U.S. English, which advocates making English the official U.S. language, say outreach efforts should be curtailed.
"Unless we are going to put things out in 300 languages, we should do everything in English and put that extra money we save to help you learn English," spokesman Rob Toonkel said.
Chinese is the language spoken most besides Spanish, with 2 million people speaking it at home. It was followed by French (1.6 million), German (1.4 million) and Tagalog (1.2 million).
The number who spoke Russian increased the most during the 1990s, nearly tripling to 706,000. That reflected a rise in Russian immigration over the decade, the first since the fall of the Soviet Union.