Over 4000 sites recognized, but I didn't find an online list. But it seems I saw a paper version once upon a time.
"The Family Land Heritage Program honors farms and ranches that have been in continuous agricultural operation by the same family for 100 years or more. The program is designed to recognize and chronicle the unique history of Texas agriculture and the men and women who settled this great state and continue the tradition today.
Since the program started in 1974, the Texas Department of Agriculture has recognized more than 4,200 farms and ranches in 232 counties across Texas. "
A map at Family Land Heritage Honorees By County Map 1974-2006 can help.