Question:
Who was the head of Chicago in Dec, 1869?

Context:
 Roswell B. Mason is the head of the government of Chicago from Jan, 1869 to Jan, 1871. 
 Walter Smith Gurnee is the head of the government of Chicago from Jan, 1851 to Jan, 1853. 
 Michael Anthony Bilandic is the head of the government of Chicago from Dec, 1976 to Apr, 1979. 
 DeWitt Clinton Cregier is the head of the government of Chicago from Jan, 1889 to Jan, 1891. 
 Augustus Garrett is the head of the government of Chicago from Jan, 1845 to Jan, 1846. 
 Monroe Heath is the head of the government of Chicago from Jan, 1876 to Jan, 1879. 
 Alson Sherman is the head of the government of Chicago from Jan, 1844 to Jan, 1845. 
 John A. Roche is the head of the government of Chicago from Jan, 1887 to Jan, 1889. 
 Julian Sidney Rumsey is the head of the government of Chicago from Jan, 1861 to Jan, 1862. 
 Hempstead Washburne is the head of the government of Chicago from Jan, 1891 to Jan, 1893. 
 George Bell Swift is the head of the government of Chicago from Apr, 1895 to Jan, 1897. 
 Charles McNeill Gray is the head of the government of Chicago from Jan, 1853 to Jan, 1854. 
 James Hutchinson Woodworth is the head of the government of Chicago from Jan, 1848 to Jan, 1850. 
 Rahm Emanuel is the head of the government of Chicago from May, 2011 to May, 2019. 
 Anton Cermak is the head of the government of Chicago from Apr, 1931 to Mar, 1933. 
 Joseph Medill is the head of the government of Chicago from Jan, 1871 to Sep, 1873. 
 John Charles Haines is the head of the government of Chicago from Jan, 1858 to Jan, 1860. 
 Edward Joseph Kelly is the head of the government of Chicago from Apr, 1933 to Apr, 1947. 
 Isaac Lawrence Milliken is the head of the government of Chicago from Jan, 1854 to Jan, 1855. 
 John Blake Rice is the head of the government of Chicago from Jan, 1865 to Jan, 1869. 
 Carter Harrison is the head of the government of Chicago from Jan, 1893 to Oct, 1893. 
 Lori Lightfoot is the head of the government of Chicago from May, 2019 to Dec, 2022. 
 Alexander Loyd is the head of the government of Chicago from Jan, 1840 to Jan, 1841. 
 Harvey Doolittle Colvin is the head of the government of Chicago from Dec, 1873 to Jan, 1875. 
 William Hale Thompson is the head of the government of Chicago from Jan, 1927 to Jan, 1931. 
 Edward Fitzsimmons Dunne is the head of the government of Chicago from Jan, 1905 to Jan, 1907. 
 John Patrick Hopkins is the head of the government of Chicago from Dec, 1893 to Jan, 1895. 
 William Butler Ogden is the head of the government of Chicago from Jan, 1837 to Jan, 1838. 
 Lester L. Bond is the head of the government of Chicago from Aug, 1873 to Dec, 1873. 
 John Wentworth is the head of the government of Chicago from Jan, 1860 to Jan, 1861. 
 Richard J. Daley is the head of the government of Chicago from Apr, 1955 to Dec, 1976. 
 Harold Washington is the head of the government of Chicago from Apr, 1983 to Nov, 1987. 
 Eugene Sawyer is the head of the government of Chicago from Dec, 1987 to Apr, 1989. 
 Martin H. Kennelly is the head of the government of Chicago from Apr, 1947 to Apr, 1955. 
 Richard M. Daley is the head of the government of Chicago from Apr, 1989 to May, 2011. 
 John Putnam Chapin is the head of the government of Chicago from Jan, 1846 to Jan, 1847. 
 Benjamin Wright Raymond is the head of the government of Chicago from Jan, 1842 to Jan, 1843. 
 Buckner Stith Morris is the head of the government of Chicago from Jan, 1838 to Jan, 1839. 
 Carter Harrison is the head of the government of Chicago from Jan, 1911 to Jan, 1915. 
 Francis Cornwall Sherman is the head of the government of Chicago from Jan, 1862 to Jan, 1865. 
 William Emmett Dever is the head of the government of Chicago from Jan, 1923 to Jan, 1927. 
 Frank J. Corr is the head of the government of Chicago from Mar, 1933 to Apr, 1933. 
 Fred A. Busse is the head of the government of Chicago from Jan, 1907 to Jan, 1911. 
 Levi Day Boone is the head of the government of Chicago from Jan, 1855 to Jan, 1856. 
 David Duvall Orr is the head of the government of Chicago from Nov, 1987 to Dec, 1987.

Answer:
Roswell B. Mason