They do foreclose on vacant land...but not often in the same way as homes, because bare land is not financed as often, and when it is, there is usually substanital down payment, like 50%. However, tax deed sales are a real possibility for someone looking for bargain priced land. Many auction houses will list quite a bit of unimproved land as well.
Many lots are available at a fraction of their former value throughout the South, Florida, Texas, Great Lakes areas...to name a few, primarily because many developers lost their shirts mid-development and there are planned communities where virtually hundreds of the unsold lots have been turned over to the counties for past due taxes. Buyer beware - there are, naturally, a number of "get rich quick" schemes and scams of worthless parcels being marketed by shady operators too. But real deals exist.
My best advice - first decide where you want to look - and know why. Is there an upside potential for growth? What is the historical pattern? How is the employment outlook? Is there some reason why baby-boomers are targeting the area, and likely to continue to do so after the recession lifts? Then find a good local agent who has land listings, and tends to deal in land. Most agents don't. You can find them on Trulia...Realtor.com...most of the sites, by looking at the "land" listings.