Under President Obama's estate tax proposal (with a $3.5 million per person exemption), there would be sixty-one taxable estates in Colorado in 2011, including just one estate that was a small farm or business estate. Nationally, "in 2011, there would be 6,160 taxable estates of which about 100 would be small farms and businesses."
A small farm or business estate is defined as one where a majority of the estate assets are in farm or business form, and the farm or business is worth $5,000,000 or less.
Farms would make up a fairly modest minority of the estate taxable small farm and business estates. You could probably count the number in the country as a whole in any given year on your fingers.