He then retired from business at age eighty. Yonge founded a demonstration farm and ranch called Magnolia Farms in 1899, located twenty miles northwest of Pensacola along the Perdido River near Muscogee, but just over the Alabama state line. This enterprise was owned by the Southern States Lumber Company under the supervision of himself and Oscar Williams, its superintendent, and later included a dairy that eventually developed one of the South's premier herds of Jersey dairy cattle. With consolidation of Florida state schools in 1905, Yonge was appointed a member of their Board of Control, the governing body of the state university system of Florida. He served, except for one term, until his retirement in 1933 at the age of eighty-three, and was its chairman for the last twenty years. Yonge was a charter member of the reorganized Florida Historical Society in 1902 and served as its president from 1932 until his death in 1934. He was an active collector of Florida historical materials and assembled a vast collection of books and documents that his son, Julien C. Yonge, inherited and further expanded. Julien Yonge later donated the collection, which formed the nucleus of the P.K. Yonge Library of Florida History, to the University of Florida. Yonge's wife, Lucie C. Davis, died in 1932. A life-long member of the Episcopal Church, he was survived by five of his nine children. Yonge died in Pensacola on August 9, 1934, and was buried there in St. Michael's cemetery  P. K. Yonge was designated a Great Floridian by the Florida Department of State in the Great Floridians 2000 Program. A plaque attesting to the honor is located at the Florida Department of Law Enforcement (formerly the P.K. Yonge School), on Palafox Street in Pensacola.