The Alameda County Waste Management Authority said reusable bags or those made of recycled paper can still be distributed but at a minimum charge of 10 cents per bag. That fee can be pocketed by the stores.
The new law doesn't affect grocers and retailers in San Ramon and other stores in Contra Costa County, which has not signed onto the ban.
Alameda County joins other parts of the Bay Area, including San Francisco, San Jose and San Mateo, that have already established similar ordinances.
Alameda County anticipates the program, which was adopted in January 2012, will save on the cost of litter and storm drain cleanup, which costs the county about $24 million per year.
"By limiting the distribution of single-use bags and urging people to bring reusable bags, we expect to see far fewer plastic bags littering our cities in future years," Waste Management Authority's executive director Gary Wolff said. "One reusable bag can replace as many as 600 single-use bags."
Stores affected by the ban will still be allowed to provide plastic bags for produce, bulk food or meat from within the store. Restaurants and take-out food restaurants are also exempt from the ordinance.
WIC and food stamp customers won't have to pay the 10-cent fee for paper bags.
All 14 cities within the county and unincorporated Alameda County are affected by the countywide ban.