Table:
text: United States Ambassador to Mexico
List of ambassadors
List of ambassadors
Representative Title From_ To_ Appointed_by_
Richard S. Spofford Special Diplomatic Agent 1854  Franklin Pierce
John Forsyth Jr. Minister 1856 1858 Franklin Pierce
William M. Churchwell Special Diplomatic Agent 1858  James Buchanan
Alfred Mordecai Special Diplomatic Agent 1858  James Buchanan
Duff Green Special Diplomatic Agent 1859  James Buchanan
David R. Porter Special Diplomatic Agent 1859  James Buchanan
Robert Milligan McLane Minister 1859 1860 James Buchanan
Henry Roy de la Reintrie Special Diplomatic Agent 1860  James Buchanan
John B. Weller Minister 1860 1861 James Buchanan
Thomas Corwin Minister 1861 1864 
Robert W. Shufelt Special Diplomatic Agent 1862  Abraham Lincoln
Lewis D. Campbell Minister 1866 1867 Andrew Johnson
Marcus Otterbourg Minister 1867  Andrew Johnson

text: United States Ambassador to Mexico
List of ambassadors
List of ambassadors
Representative Title From_ To_ Appointed_by_
William S. Rosecrans Minister 1868 1869 Andrew Johnson
Thomas H. Nelson Minister 1869 1873 
John W. Foster Minister 1873 1880 Ulysses S. Grant
Philip Hicky Morgan Minister 1880 1885 Rutherford B. Hayes
Henry R. Jackson Minister 1885 1886 
Thomas Courtland Manning Minister 1886 1887 Grover Cleveland
Edward S. Bragg Minister 1888 1889 Grover Cleveland
Thomas Ryan Minister 1889 1893 
Isaac P. Gray Minister 1893 1895 
Matt Whitaker Ransom Minister 1895 1897 Grover Cleveland
Powell Clayton Minister 1897 1898 

text: United States Ambassador to Mexico
List of ambassadors
List of ambassadors
Representative Title From_ To_ Appointed_by_
William Shaler Special Diplomatic Agent 1810 1812 James Madison
John H. Robinson Special Diplomatic Agent 1812 1814 James Madison
Joel Roberts Poinsett Minister 1825 1829 John Quincy Adams
Anthony Butler Special Diplomatic Agent 1829  
Anthony Butler Chargé d`Affaires 1829 1835 
William A. Slacum Special Diplomatic Agent 1835 1836 Andrew Jackson
Powhatan Ellis Chargé d`Affaires 1836  Andrew Jackson
Robert Greenhow Special Diplomatic Agent 1837  
Powhatan Ellis Minister 1839 1842 Martin Van Buren
Henry E. Lawrence Special Diplomatic Agent 1842  John Tyler
Waddy Thompson, Jr. Minister 1842 1844 John Tyler
Moses Yale Beach Special Diplomatic Agent 1843  John Tyler

text: United States Ambassador to Mexico
List of ambassadors
List of ambassadors
Representative Title From_ To_ Appointed_by_
Gilbert L. Thompson Special Diplomatic Agent 1844  John Tyler
Wilson Shannon Minister 1844 1845 John Tyler
John Slidell Minister 1845  James K. Polk
David Conner Special Diplomatic Agent 1846  James K. Polk
Nathan Clifford Minister 1848 1849 James K. Polk
Robert P. Letcher Minister 1849 1852 
Robert Greenhow Special Diplomatic Agent 1850  
George G. Goss Special Diplomatic Agent 1850 1852 
George W. Slacum Special Diplomatic Agent 1851  Millard Fillmore
Edward Smith Special Diplomatic Agent 1852  Millard Fillmore
Alfred Conkling Minister 1852 1853 Millard Fillmore
George E. Cooper Special Diplomatic Agent 1853  
Christopher L. Ward Special Diplomatic Agent 1853  
James Gadsden Minister 1853 1856

Question: At least how many people does the United States Ambassador to Mexico hold the title of Minister?