Principal Officers and Chiefs of Mission, by year: 1866
Note: Career Foreign Service appointees are asterisked.
- Wright, Joseph Albert (1810-1867)
- Envoy Extraordinary and Minister Plenipotentiary, Germany (1857-1861)
- Envoy Extraordinary and Minister Plenipotentiary, Germany (1865-1867)
- Williams, Alpheus Starkey (1810-1878)
- Minister Resident, El Salvador (1866-1869)
- Wilson, James (1825-1867)
- Minister Resident, Venezuela (1866-1867)
- Adams, Charles Francis (1807-1886)
- Envoy Extraordinary and Minister Plenipotentiary, United Kingdom (1861-1868)
- Asboth, Alexander (1811-1868)
- Minister Resident, Argentina (1866-1868)
- Minister Resident, Uruguay (1867-1868)
- Bigelow, John (1817-1911)
- Envoy Extraordinary and Minister Plenipotentiary, France (1865-1866)
- Clay, Cassius Marcellus (1810-1903)
- Envoy Extraordinary and Minister Plenipotentiary, Spain (1861)
- Envoy Extraordinary and Minister Plenipotentiary, Russia (1861-1862)
- Envoy Extraordinary and Minister Plenipotentiary, Russia (1863-1869)
- Clay, Thomas Hart (1803-1871)
- Minister Resident, Nicaragua (1862-1863)
- Minister Resident, Honduras (1863-1866)
- Coggeshall, William Turner (1824-1867)
- Minister Resident, Ecuador (1866-1867)
- Burlingame, Anson (1820-1870)
- Envoy Extraordinary and Minister Plenipotentiary, Austria (1861)
- Envoy Extraordinary and Minister Plenipotentiary, China (1861-1867)
- Campbell, James Hepburn (1820-1895)
- Minister Resident, Sweden (1864-1867)
- Minister Resident, Colombia (1866)
- Campbell, Lewis Davis (1811-1882)
- Envoy Extraordinary and Minister Plenipotentiary, Mexico (1866)
- Dickinson, Andrew B. (?-?)
- Minister Resident, Nicaragua (1861-1863)
- Minister Resident and Extraordinary, Nicaragua (1863-1869)
- Dix, John Adams (1798-1879)
- Minister Resident, Netherlands (1866)
- Envoy Extraordinary and Minister Plenipotentiary, France (1866-1869)
- Ewing, Hugh Boyle (1826-1905)
- Minister Resident, Netherlands (1866-1870)
- Hale, Charles (1831-1882)
- Agent/Consul General, Egypt (1864-1870)
- Assistant Secretary of State (1872-1873)
- Hale, John Parker (1806-1873)
- Envoy Extraordinary and Minister Plenipotentiary, Spain (1865-1869)
- Hall, Allen A. (?-1867)
- Minister Resident, Bolivia (1863-1867)
- Hanson, Abraham (?-1866)
- Commissioner and Consul General, Liberia (1863-1866)
- Harrington, George (1815-1892)
- Minister Resident, Switzerland (1865-1869)
- Harvey, James E. (1820-?)
- Minister Resident, Portugal (1861-1869)
- Hassaurek, Frederick (Friedrich) (1831-1885)
- Minister Resident, Ecuador (1861-1866)
- Hovey, Alvin Peterson (1821-1891)
- Envoy Extraordinary and Minister Plenipotentiary, Peru (1865-1870)
- Hunter, William (1805-1886)
- Chief Clerk (1852-1855)
- Secretary of State ad interim (1853)
- Assistant Secretary of State (1855)
- Secretary of State ad interim (1860)
- Second Assistant Secretary of State (1866-1886)
- Kilpatrick, Judson (1836-1881)
- Envoy Extraordinary and Minister Plenipotentiary, Chile (1865-1870)
- Envoy Extraordinary and Minister Plenipotentiary, Chile (1881)
- King, Rufus (1814-1876)
- Minister Resident, Holy See (1861)
- Minister Resident, Holy See (1863-1867)
- Kirk, Robert C. (1821-?)
- Minister Resident, Argentina (1862-1866)
- Minister Resident, Uruguay (1869-1870)
- Minister Resident, Argentina (1869-1871)
- Marsh, George Perkins (1801-1882)
- Minister Resident, Turkey (1849-1853)
- Envoy Extraordinary and Minister Plenipotentiary, Italy (1861-1882)
- McBride, James (1802-1875)
- Minister Resident, Hawaii (1863-1866)
- McCook, Edward Moody (1833-1909)
- Minister Resident, Hawaii (1866-1868)
- McGinnis, John (?-?)
- Minister Resident, Sweden (1866)
- Lawrence, Albert Gallatin (1836-1887)
- Minister Resident, Costa Rica (1866-1868)
- Morris, Edward Joy (1815-1881)
- Chargé d'Affaires, Two Sicilies (1850-1853)
- Minister Resident, Turkey (1861-1870)
- Motley, John Lothrop (1814-1877)
- Ambassador Extraordinary and Plenipotentiary, Austria (1861-1867)
- Ambassador Extraordinary and Plenipotentiary, United Kingdom (1869-1870)
- Nelson, Thomas Henry (1824-1896)
- Envoy Extraordinary and Minister Plenipotentiary, Chile (1861-1866)
- Envoy Extraordinary and Minister Plenipotentiary, Mexico (1869-1873)
- Peck, Henry Everard (1821-1867)
- Commissioner and Consul General, Haiti (1865)
- Minister Resident/Consul General, Haiti (1866-1867)
- Pike, James Shepard (1811-1882)
- Minister Resident, Netherlands (1861-1866)
- Rhodes, Albert (1840-?)
- Chargé d'Affaires, Netherlands (1866)
- Riotte, Charles N. (?-?)
- Minister Resident, Costa Rica (1861-1867)
- Minister Resident, Nicaragua (1861-1867)
- Minister Resident, Costa Rica (Not commissioned; nomination tabled by the Senate.)
- Rousseau, Richard Hilaire (1815-1872)
- Minister Resident, Honduras (1866-1869)
- Sanford, Henry Shelton (1823-1891)
- Minister Resident, Belgium (1861-1869)
- Minister Resident, Belgium (Not commissioned; nomination not confirmed by the Senate.)
- Minister Resident, Spain (Not commissioned; nomination not confirmed by the Senate.)
- Seward, Frederick William (1830-1915)
- Assistant Secretary of State (1861-1869)
- Assistant Secretary of State (1877-1879)
- Seward, William Henry (1801-1872)
- Secretary of State (1861-1869)
- Seys, John (?-?)
- Minister Resident/Consul General, Liberia (1866-1870)
- Sickles, Daniel Edgar (1825-1914)
- Minister Resident, Netherlands (1866)
- Envoy Extraordinary and Minister Plenipotentiary, Spain (1869)
- Van Valkenburgh, Robert Bruce (1821-1888)
- Minister Resident, Japan (1866-1869)
- Warren, Fitz Henry (1816-1878)
- Minister Resident, Guatemala (1865-1869)
- Washburn, Charles Ames (1822-1889)
- Commissioner, Paraguay (1861)
- Minister Resident, Paraguay (1863-1868)
- Webb, James Watson (1802-1884)
- Chargé d'Affaires, Austria (1849-1850)
- Minister Resident, Turkey (1861)
- Envoy Extraordinary and Minister Plenipotentiary, Brazil (1861-1869)
- Yeaman, George Helm (1829-1908)
- Minister Resident, Denmark (1865-1870)