Balad police Lieutenant-Colonel Adel Abdallah said bombs went off about 6.45pm local time on Thursday near a busy market in a predominantly Shia district, in the town about 80km north of Baghdad, killing at least 85 and wounding more than 110.
The car bombs hit a bank, a vegetable market and another location, witnesses said.
Dr Khaled al-Azawi of Balad Hospital said the dead included the town's police chief, Col Kadhim Abdul Razzaq, and four other policemen.
Meanwhile, a roadside bomb killed five American soldiers during combat in the western town of Ramadi, the US military said on Thursday.
The five, who were assigned to the 2nd Marine Division, II Marine Expeditionary Force, were hit while "conducting combat operations" on Wednesday, a statement by the Marines said.
Five US soldiers were killed in
Ramadi on Wednesday
The blast was the deadliest single attack on US forces in Iraqi since a roadside bomb killed 14 marines near the city of Haditha in Anbar province in western Iraq on 3 August.
Thirteen US service members have now been killed in Iraq over the past four days.
Wednesday's attack brought to 1934 the number of US service members who have died since the Iraq war started in March 2003, according to an Associated Press count.
It also raised the number of people who have died in violence in Iraq this week to more than 100.