A report from the Pew Hispanic Center estimates the number of illegal immigrants in the country decreased nearly 10 percent since 2007.
But Oklahoma numbers didn't change much. In fact, they appear to have risen from 55,000 in 2008 to 60,000 in 2009. The state population is about 3.6 million.
The report's authors said the increase falls within the study's margin of error and could be a result of sampling anomalies rather than an actual increase in the population.
"Since 2000, there hasn't been much change in Oklahoma," said the study's senior demographer, Jeffrey Passel.
Nationally, the number shifted from 11.1 million in March 2009 from a peak of 12 million in March 2007.
It's the first significant reversal in the growth of the illegal immigrant population in 20 years, the report states.
From 1990 until 2000, the undocumented population in the state increased 70 percent from 15,000 to about 50,000, report estimates show.
Passel said Oklahoma likely is affected by a large undocumented population in neighboring Texas, where 1.6 million illegal immigrants make up 6.5 percent of the state's population.
"When we look at regional patterns, Oklahoma is swamped by what is happening in Texas," Passel said.
California, Nevada, Texas and Arizona maintain the highest percentage as a portion of the population, estimates show. Nevada, California, Texas and New Jersey had the largest share of immigrants in the labor force.