A new report by Fairfax County executives says the cost of delivering government services to undocumented immigrants in the county is pretty much impossible to know.

That's according to County Executive Anthony Griffin, in a report made public Monday.

The report says that nobody knows how many undocumented immigrants live in Fairfax County. It also notes that many of the services like libraries, parks and public transit, are already there for everyone and not for a specific group in the population.

The county was able to determine one cost, though: the cost of housing undocumented immigrants in the county jail, which will cost the sheriff's office nearly $4 million this fiscal year.

Earlier this year, Prince William County Executive Craig Gerhart told lawmakers that he couldn't provide an accurate or dependable answer about the cost to serve the undocumented population.

Loudoun County administrators told their Board of Supervisors essentially the same thing in September. Those two counties have passed resolutions to deny services to illegal immigrants.