FARGO (AP) - New Census Bureau estimates show West Fargo was North Dakota's fastest-growing city last year.

West Fargo grew 10 percent during the year ending last July, to 21,508 people, the figures released Thursday show. Neighboring Fargo dropped 0.4 percent to 90,056. Cass County continued to grow during the year, although not as rapidly as in the past, the State Data Center said.

Thirty-seven cities in the state showed growth.

Bismarck grew 1.3 percent last year, to an estimated 58,833 people in July 2006. That was up 759 residents from 2005, and up 5 percent, or 2,801 residents, from 2000.

Bismarck planner Carl Hokenstad attributed the city increase to growth in Morton and Burleigh counties, which together reached the 100,000 population mark.

"I can't explain it, but it's almost like we jumped up on the radar screen of a lot of national companies," Hokenstad said. "Maybe it's just a lot of various things that have come together at one time. It kind of provides a momentum."

Neighboring Mandan saw its population grow by 247, to 17,449 in 2006, according to the estimates.

Grand Forks' new estimate is 50,372, up 587 residents from 2005. The city's population estimates have fluctuated since 2000, and city officials have disputed the Census Bureau figures.

Williston's 2006 estimate of 12,303 is up 117 residents, or 0.9 percent, from 2005. The increase does not offset a decline between 2000 and 2004, but it is the second year of growth from increased oil activity in western North Dakota.

Other cities with increases included Jamestown, Watford City, Wildrose, Arnegard, Ray, Tioga, Killdeer, Dunseith, Rolette, Rolla and Riverdale.

Minot's estimated population slipped to 34,745, down about 0.6 percent, or 202 residents, from 2005. City Manager David Waind said he believes Minot has grown, despite the estimates.

"I am convinced that they are off and fairly substantially off," he said. "For us to prove it will take another census. … I am absolutely convinced that when the 2010 census comes around that we won't have lost population."

Waind said the city still advertises its population at 36,567.