The Times just published another of its fascinating interactive maps of Census data.
The current map plots a variety of data points for every county in the US, based on 2010 Census data. One data point is the number of occupied housing units.
Cook County, which saw its population declined by 3.4% over the last decade, also saw an 0.4% decline in the number of occupied housing units. The number of vacant units increased by 75.5%, to 214,003.