Hogsed said Cobb included foreclosures and distressed sales.
When DeKalb re-sent notices earlier this week, they lowered values for 95,000 parcels. Gwinnett and Clayton both lowered values for about 70,000.
Fulton plans to cut taxable values for about 100,000 parcels when it mails notices on June 5.
Hogsed said Cobb's reductions may be so much lower because it had not revalued about 150,000 residential parcels since 2006. So, Hogsed noted, many of those may not have been at the peak of the market when the crash came. He added that, while foreclosures are up, the county only had about 3,500 last year.
"We have analzyed the Cobb market more than we ever have before," Hogsed said.
Hogsed plans to mail a second round of notices June 10. But he said those 6,000 notices won't all be lowering values. In all, he said about two-thirds of Cobb's 20,000 notices will lower values. The rest will either raise the value or reject a property tax return asking for a lower value.
Only about 6 percent of Cobb's 246,000 parcels will fall in value. Owners of property around Powder Springs and Austell are most likely to get one of the notices.