Public access was limited Monday to the downtown building where the commissioners meet, a structure formerly known as the Texas School Book Depository, after law enforcement personnel and vehicles were seen outside the office of John Wiley Price.
The commissioner, who has held office for a quarter century, said he didn't know the reason for the search but suspected it had to do with his history as a community activist.
"Twenty-seven years I've been in this office, and it's not the first time I've come up against this kind of adversity," he said.
Price, 61, has engaged in numerous public protests, most aimed at improving minority employment. Several have led to his arrest.
Price's attorney, Billy Ravkind, said the FBI declined to tell him when it would unseal the affidavit supporting the search warrant. He said the warrants ask for "everything in the (federal) criminal code."
The veteran criminal defense attorney said he's learned some information about the case from witnesses and that those allegations are "bull." He declined to be more specific but added that the searches are worrisome for Price.
"Anyone would be concerned if 20-plus agents dropped down and visited your office," Ravkind told The Associated Press.
The Dallas Morning News said Ravkind provided it with copies of search warrants issued for Price's person and two vehicles, but not copies of other warrants for his home and office. The warrants said agents sought all electronic data from 2001 to the present related to alleged violations of federal charges ranging from bribery and tax evasion to money laundering and structuring of transactions to evade reporting requirements.
FBI spokeswoman Beverly Esselbach said she could confirm that agents were at locations in the Dallas area shown in televised reports. However, she said she couldn't make any other statements about the case.
The searches occurred on the same day as the inauguration of newly elected Dallas Mayor Mike Rawlings, who received strong support from Price.
Dallas television station WFAA reported that, in 2009, then-Dallas County Judge Jim Foster revealed under oath that Price had been the subject of an FBI probe dating to the previous fall over a huge inland port development in southern Dallas County.
Foster, who lost his bid for re-election to Clay Jenkins last year, answered questions involving an alleged "shakedown" by Price during a deposition earlier this month, the TV station reported. Foster told WFAA he had talked to FBI agents concerning Price "on many occasions."