Forty-five percent of the nation's 3,141 counties lost population in the 1980s and the Midwest was hardest hit by the losses.

Sixty-three percent of counties in the Midwest lost population, compared with 39 percent in the South, 30 percent in the West and 27 percent in the Northeast, the Census Bureau said Monday.In the Intermountain West, Salt Lake County's population was listed at 725,956 for 55th place, three places behind Clark County, Nev., with a population of 741,459. Clark County showed a 60.1 percent gain during the past decade. Salt Lake County's population increased 17.3 percent.

Here are some other facts concerning counties from the 1990 census:

-Thirty counties had a million or more people in 1990. That's five more than in 1980.

-Los Angeles County was the nation's largest, with 8.9 million people, followed by Cook County, Ill., at 5.1 million and Harris County, Texas, at 2.8 million. Chicago is in Cook County and Houston is in Harris.

-Los Angeles County added the most people, 1.4 million.

-The five counties of New York City all gained population for the first time since 1950.

-Nine counties lost more than one-fourth of their population. They were Platte, Wyo., and Lake, Colo., each down 32 percent; Mineral, Colo., down 31 percent; Hall and Hemphill, Texas, and Greenlee, Ariz., each down 30 percent; McDowell, W.Va., down 29 percent; Shoshone, Idaho, down 28 percent; and Dickens, Texas, down 27 percent.

-The population in eight counties more than doubled during the 1980s: Flagler, Fla., up 163 percent; Douglas, Colo., up 140 percent; Hernando, Fla., up 127 percent; Camden, Ga., up 126 percent; Matanuska-Susitna Borough, Alaska, up 123 percent; Osceola, Fla., up 119 percent; Fayette, Ga., up 115 percent; and Gwinnett, Ga., up 112 percent.

-There were 458 counties with at least 100,000 people.

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Nation's biggest counties

County, State 1990 1980 % Chg

Los Angeles, Calif. 8,863,164 7,477,238 18.5

Cook, Ill. 5,105,067 5,253,628 -2.8

Harris, Texas 2,818,199 2,409,547 17.0

San Diego, Calif. 2,498,016 1,861,846 34.2

Orange, Calif. 2,410,556 1,932,921 24.7

Kings, N.Y. 2,300,664 2,231,028 3.1

Maricopa, Ariz. 2,122,101 1,509,175 40.6

Wayne, Mich. 2,111,687 2,337,843 -9.7

Queens, N.Y. 1,951,598 1,891,325 3.2

Dade, Fla. 1,937,094 1,625,509 19.2

Dallas, Texas 1,852,810 1,556,419 19.0

Philadelphia, Pa. 1,585,577 1,688,210 -6.1

King, Wash. 1,507,319 1,269,898 18.7

Santa Clara, Calif. 1,497,577 1,295,071 15.6

New York, N.Y. 1,487,536 1,428,285 4.1

San Bernardino, Cal. 1,418,380 895,016 58.5

Cuyahoga, Ohio 1,412,140 1,498,400 -5.8

Middlesex, Mass. 1,398,468 1,367,034 2.3

Allegheny, Pa. 1,336,449 1,450,195 -7.8

Suffolk, N.Y. 1,321,864 1,284,231 2.9

Nassau, N.Y. 1,287,348 1,321,582 -2.6

Alameda, Calif. 1,279,182 1,105,379 15.7

Broward, Fla. 1,255,488 1,018,257 23.3

Bronx, N.Y. 1,203,789 1,168,972 3.0

Bexar, Texas 1,185,394 988,971 19.9

Riverside, Cal. 1,170,413 663,199 76.5

Tarrant, Texas 1,170,103 860,880 35.9

Oakland, Mich. 1,083,592 1,011,793 7.1

Sacramento, Calif. 1,041,219 783,381 32.9

Hennepin, Minn. 1,032,431 941,411 9.7