Daggett County, with 700 residents, has the 10th smallest population of any of the United States' 3,139 counties, the Census Bureau reported Friday.

The bureau's year-end report also showed that Utah's Millard County ranked 12th in growth, at 58.6 percent. Although Millard had an increase in households of 55.5 percent to rank 11th, the county's 16.4 percent decrease in civilian labor growth between 1985 and 1986 was the eighth largest such decline.By contrast, Washington County had the 17th highest growth rate in civilian labor force at 13.7 percent. Washington County also ranked 20th in population growth between 1980 and 1986 with a 48.2 percent increase.

Utah had nine counties - the most of any state - among the highest 25 for percentage of the population under five years of age in 1984. Uintah County was second highest in the U.S. with 14.9 percent under the age of 5; followed by Box Elder and Davis Counties, 13.9; Cache County, 13; Utah County, 12.6; Tooele County, 12.5; Salt Lake and Washington Counties, 12.1; and Carbon County, 12.