Cornelius Ambrose Logan (August 24, 1832 – January 30, 1899) was an American physician, writer, and diplomat, best known for his two terms as United States Ambassador to Chile (1873-6 and 1882-5) during difficult times. Logan was a member of the Independent Order of Odd Fellows; he organized the first grand lodge of Odd Fellows in Kansas and served as Grand Sire of the national organization 1872–4. While in Chile he organized the first lodge and Grand Lodge there, in Valparaiso.