O.C. Ranks 5th in Country’s Top Counties : Census: Orange County’s population of 2.4 million people falls behind Los Angeles’, which still remains the nation’s largest, and San Diego’s.

Orange County grew by 25% during the 1980s, but it still slipped a notch in the rankings of the country’s most populous counties, according to a Census Bureau report released Monday.

The county now ranks fifth, with 2.4 million people, after being passed by San Diego County, which has a population of 2.5 million. San Diego County grew by 34% since the 1980 census.

For the first time, Southern California’s population explosion has made the region home to three of the nation’s five largest counties, according to the report.

Los Angeles County, with a population of more than 8.8 million, retains its 1980 rank as the nation’s largest county.

Holding on to second and third places are Chicago’s Cook County, with 5.1 million people, and Houston’s Harris County, with 2.8 million.

Detroit’s Wayne County, which had been fourth, slipped to eighth, and Brooklyn’s Kings County fell from fifth to sixth.

In all, the United States has 458 counties with populations of 100,000 or more. Of those, 30 have 1 million residents or more. Eight of the 30 are in California and five of those are in Southern California. Six of the top 30 are in New York and four are in Texas.

California’s most populous counties also include San Bernardino, with just over 1.4 million; Riverside, just under 1.2 million; Santa Clara, just under 1.5 million; Alameda, just under 1.3 million; and Sacramento, just over 1 million.

San Bernardino, Riverside and Sacramento counties all passed the 1 million mark during the past decade. Riverside, which grew 76.5%, and San Bernardino, which grew 58.5%, were the fastest growing of the country’s 30 largest counties.

Although the growth rate for Los Angeles County was 18.5%, it gained more residents than any other county in the country, with a rise of 1.4 million. San Diego was second, increasing 636,000, and Phoenix’s Maricopa County was third with a gain of about 613,000.

In Los Angeles, Orange and San Diego counties, the growth was largely because of a tremendous influx of Latinos and Asians, according to the report.

The Anglo share of the population declined 8% in Los Angeles County, while it grew 3% in Orange County and 19% in San Diego County. The black population grew 1% in Los Angeles County, 60% in Orange County and 47% in San Diego County.

Population growth in San Bernardino and Riverside counties was spread somewhat more evenly among all ethnic groups, although Anglo growth lagged well behind that of Latinos, Asians and blacks.