An index that measures how many homeowners are underwater on their mortgages fell for the third consecutive quarter but the decrease was more attributed to completed foreclosures than any gain in home values.

About 10.8 million U.S. homes, or 22.5 percent of all homes with mortgages had negative equity, meaning the homeowner owed more on the mortgage than the home was worth at the end of the third quarter, data provider CoreLogic said Monday. That compares with 11 million properties, or 23 percent of all homes in the second quarter.

Another 2.4 million borrowers were considered to possess near-negative equity mortgages, because the equity in their homes was less than 5 percent.

In Illinois during the third quarter, 19.7 percent of homes with mortgages were underwater and another 5 percent were in a near-negative equity position.

While the number of borrowers with negative equity dropped by half a million in the first nine months of 2010, CoreLogic said the nation’s homeownership rate is actually lower than the U.S. Census Bureau’s count because the federal government’s statistics include those borrowers who are severely underwater.

If homeowners with severe negative equity are excluded from the definition of homeowner, the nation’s homeownership rate is 62.4 percent, according to CoreLogic.