One of Virginia's fastest growing counties wants to know how much money illegal immigration is costing the county government, and may send a bill to the federal government for the extra costs.

The Prince William Board of County Supervisors has asked county staff to complete the study by January 16th.

About 20 percent of county residents are foreign-born. Supervisors say the problem is driving up costs for schools, healthcare, law enforcement and social services.

The study was proposed by Supervisor WS Covington the Third. He says he's realistic enough to know the county probably won't see a penny in reimbursement from the federal government. He calls his proposal "more symbolic."

The National Council of La Raza, the country's oldest and largest Hispanic civil rights organization, is welcoming the county's attempt to study the issue, if the study is "based on sound methodology and it is unbiased." That's according to Michele Waslin, the group's director of immigration policy.