Fourteen Democratic candidates and one Republican are vying for the seat.
Johnson resigned in July, months after being arrested during a widespread corruption investigation by the FBI that also involved the arrest of her husband, former county executive Jack B. Johnson.
Leslie Johnson, who stuffed $79,600 in her underwear and flushed a $100,000 check from a developer down a toilet, pleaded guilty to destroying evidence. The couple are awaiting sentencing on federal charges.
The new council member, who will represent one of the county’s largest districts, is likely to play an important role in shaping policy involving economic development, education and public safety.
Polls will be open from 7 a.m. to 8 p.m.
The winners of Tuesday’s special primary election will face off in the general election on Oct. 18.