Members of AFSCME Local 1028 work in a variety of county offices, including the court system and jail, health department and highway department.
Anders Lindall is an AFSCME spokesman. He says employees began walking picket lines at about two dozen locations Monday morning.
The union and county have been in contract talks for the last 15 months.
Key sticking points are cost-of-living pay raises and health insurance payments.
The office of Will County Executive Larry Walsh issued a news release Monday, indicating the County government would remain open for business, despite the strike.
"I have said throughout these negotiations that a strike is not good for anyone; no one wins with a strike," Walsh was quoted in the release. "I was very disappointed to learn that AFSCME employees who claimed they too wanted to avoid a strike wore red stickers throughout all of our recent negotiation sessions that proudly proclaimed their readiness to strike...I had hoped they would have spent their time and energy on bringing a more realistic proposal on health care and wages to the bargaining table."
A federal mediator has been assigned to the dispute for months and could call the sides back together.