From the official site here:
http://www.conn-selmer.com/en-us/abo...-numbers/conn/

1876 - 1900
Date Serial #
1876 1
1877 700
1878 1,700
1879 3,000
1880 5,000
1881 6,000
1882 7,000
1883 8,000
1884 9,000
1885 10,500
1886 12,000
1887 13,000
1888 14,000
1889 16,500
1890 18,000
1891 20,000
1892 22,500
1893 25,000
1894 27,500
1895 29,000
1896 34,000
1897 40,000
1898 46,700
1899 52,000
1900 58,000
Cup Mouthpiece Instruments
1901 - 1930
Date Serial #
1901 66,700
1902 71,000
1903 76,000
1904 82,000
1905 88,000
1906 94,000
1907 100,000
1908 106,000
1909 111,000
1910 116,000
1911 121,000
1912 126,000
1913 130,150
1914 132,400
1915 137,000
1916 142,575
1917 146,600
1918 155,000
1919 165,900
1920 169,500
1921 175,500
1922 190,450
1923 198,475
1924 206,700
1925 219,850
1926 230,900
1927 239,500
1928 252,900
1929 263,200
1930 273,700
Cup Mouthpiece Instruments
1931 - 1956
Date Serial #
1931 280,130
1932 281,360
1933 289,743
1934 294,687
1935 300,690
1936 307,996
1937 315,575
1938 322,650
1939 324,859
1940 327,850
1941 338,500
1942 348,150
1943 354,600
1944 355,500
1945 355,750
1946 355,850
1947 366,650
1948 376,100
1949 383,650
1950 389,600
1951 396,300
1952 393,301
1953 420,057
1954 427,301
1955 500,001
1956 571,850
Conn Cup Mouthpiece & Reed Instruments
1957 - 1972
Date Serial #
1957 652002
1958 718626
1959 779657
1960 834200
1961 898556
1962 949465
1963 c00501
1964 c73854
1965 e54106
1966 h31247
1967 k35274
1968 l20454
1969 "m" prefix
1970 "n" prefix
1971 "p" prefix
1972 "r" prefix
Conn Cup Mouthpiece Instruments
1973 - present
Date Serial #
1973 ga30000
1974 ga40000
1975 ga50000
1977 ga60000
1978 ga70000
1979 ga80000
1980 *
1981 *
1982 16500 - 23430*
1983 23431 - 33388*
1984 33389 - 45521*
1985 45522 - 58991*
58992 � 68841*
1987 68842 � 76617* & prefix "37"
1988 76618 � 81115* & prefix "38"
1989 prefix "39"
1990 prefix "40"
Note: From 1987 to present, add 50 to the serial number prefix to calculate the year of manufacture.