North Dakota ended the decade with more than 430,000 workers, up more than 61,000 since 2000 and an increase equal to the population of Bismarck, the state's second biggest city, a Job Service analysis showed.

Thousands of jobs remain unfilled in a state that's enjoying a robust economy thanks to its booming oil patch and healthy agriculture markets, the agency said.

While North Dakota lost residents for decades, it has gained population and jobs as oil production has increased in the past few years.

"Oil is not the only game in town, but they are important to us," said Michael Ziesch, a Job Service North Dakota research analyst.

The state added 17,755 jobs from 2008 to 2010, more than two-thirds of which were filled by workers from elsewhere. They came from every state in the nation, led by neighboring Minnesota, Montana and South Dakota, Job Service records showed.

Large influxes of workers also have come from states with similar climates and geographies as North Dakota, such as Wisconsin, Idaho and Michigan, Ziesch said. Residents from states with strong energy sectors such as Texas, Wyoming and Colorado also have flocked to North Dakota to fill jobs, he said.

In May, the state had the lowest unemployment rate in the nation at 3 percent and tallied 15,205 unfilled jobs, Ziesch said. About a third of the job openings were in the state's 17 oil-producing counties, he said.

North Dakota's overall population increased 4.7 percent from 2000 to 2010 to nearly 672,600 residents, according to the U.S. Census Bureau said. The number of workers on employers' payrolls rose 16.6 percent during the same time.

Some state officials have disputed the census estimate as too conservative. Ziesch and Richard Rathge, the state Data Center director and North Dakota demographer, said the census did not count all people working in North Dakota as residents.

Many new workers, especially those in the oil patch, don't have a permanent residence and still claim their home state, Rathge said.

"They may be living in a truck, trailer or man camp," he said.

Rathge said while North Dakota is enjoying job growth, the average salary of just more than $45,200 was 20.6 percent below the national average of about $57,000 in 2009, the latest figures available.

Only Idaho, Mississippi, Montana and South Dakota had lower average salaries than North Dakota, he said.

But with its booming economy and job growth, North Dakota is on pace to soon match the national average for the first time in more than two decades, Rathge said.

"While the national economy is struggling, North Dakota's is robust and closing the gap," he said. "North Dakota is just going gangbusters."