Historic Property often uses the definition of 'antique' - any property having a building on it that is more than 100 years old. However, increasingly, property that has some association with an historic event,  or buildings that have an association with a well-known or important figure, even from the recent pastwith or without buildings located on it, is seen as being worthy of designation as historic property, for purposes of describing it to potential buyers.
 
Notwithstanding subjective definitions of 'historic,' official historic designations and the associated programs and processes for arriving at that designation, vary worldwide. In the U.S., the National Register of Historic Places is a voluntary program administered by the U.S. Park Service. It does not provide automatic protection for a property, but can bring recognition and attention to it that would encourage and reward preservation efforts. In addition, owners of national register-listed properties may be eligible for certain kinds of tax credits for rehabilitation and restoration work. States, counties and municipalities also operate historic recognition - and in some cases protection - programs that may bring attention to, or limit changes to, historic property. Increasingly, adjacency or proximity to historic structures, sites, land and elements, e.g. cemetaries, battlefields, districts, is being advertised as part of the benefits of ownership for real estate that is so described. Many properties with historic significance remain unlisted for any number of reasons: they don't meet the criteria for listing, the owners wish to preserve their privacy, the condition is poor, or their history has not been thoroughly documented.
 
 
The following are resources:
 
http://www.nationalregisterofhistoricplaces.com/
 
http://www.nationaltrust.org/
 
http://www.nps.gov/history/heritageareas/
 
http://www.thisoldhouse.com/toh/