Good question Russ.... I think the AEDs are failry new...last 3 years and have gradually been put in place. I remember reading stories in the Sun as they were being installed and there have been one or two lifesaving stories in the paper.
From a link on the CDD website, here are the locations:
http://www.districtgov.org/slcdd/recreation/AED.asp
But, back to tkret's original point...there really should be AEDs in both squares and other larger common areas and perhaps at the country clubs.
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Maryland (DC Suburbs) - first 51 years

The Villages - next 51 years