Colorado was admitted to the Union on August 1, 1876 and elects U.S. senators to Senate class 2 and class 3.
Both of Colorados current U.S. senators are Democrats Michael Bennet (serving since 2009) and John Hickenlooper (serving since 2021). Colorado is one of fifteen states alongside Arizona, Florida, Georgia, Hawaii, Idaho, Indiana, Louisiana, Maine, Massachusetts, Minnesota, Missouri, Nevada, South Dakota and Utah to have a younger senior senator and an older junior senator.
Henry M. Teller was Colorado's longest-serving senator (1876–1882; 1885–1909).
|- style="height:2em"| colspan=3 | Vacant| Aug 1, 1876 –
Nov 15, 1876| Colorado did not elect its senators until three months after statehood.| rowspan=2 | 1| | rowspan=3 | 1| Colorado did not elect its senators until three months after statehood.| Aug 1, 1876 –
Nov 15, 1876| colspan=3 | Vacant
|- style="height:2em"! rowspan=4 | 1| rowspan=4 align=left |
Henry M. Teller| rowspan=4 | Republican| rowspan=4 nowrap | Nov 15, 1876 –
Apr 17, 1882| Elected in 1876.| rowspan=2 | Elected in 1876.Retired.| rowspan=2 nowrap | Nov 15, 1876 –
Mar 3, 1879| rowspan=2 | Republican| rowspan=2 align=right |
Jerome B. Chaffee! rowspan=2 | 1
|- style="height:2em"| rowspan=3 | Elected to next term in 1876 or 1877.Resigned to become U.S. Secretary of the Interior.| rowspan=5 | 2|
|- style="height:2em"| | rowspan=5 | 2| rowspan=5 | Elected in 1879.Lost re-nomination.| rowspan=5 nowrap | Mar 4, 1879 –
Mar 3, 1885| rowspan=5 | Republican| rowspan=5 align=right |
Nathaniel P. Hill! rowspan=5 | 2
|- style="height:2em"| rowspan=3
|- style="height:2em"! 2| align=left |
George M. Chilcott| | Republican| nowrap | Apr 17, 1882 –
Jan 27, 1883| Appointed to continue Teller's term.Did not run to finish the term.
|- style="height:2em"! 3| align=left |
Horace Tabor| | Republican| nowrap | Jan 27, 1883 –
Mar 3, 1883| Elected to finish Teller's term.Retired.
|- style="height:2em"! rowspan=3 | 4| rowspan=3 align=left |
Thomas M. Bowen| rowspan=3 | Republican| rowspan=3 nowrap | Mar 4, 1883 –
Mar 3, 1889| rowspan=3 | Election date unknown.Unknown if retired or lost re-election.| rowspan=3 | 3|
|- style="height:2em"| | rowspan=3 | 3| rowspan=3 | Elected in 1885.| rowspan=12 nowrap | Mar 4, 1885 –
Mar 3, 1909| rowspan=6 | Republican| rowspan=12 align=right |
Henry M. Teller! rowspan=12 | 3
|- style="height:2em"|
|- style="height:2em"! rowspan=6 | 5| rowspan=6 align=left |
Edward O. Wolcott| rowspan=6 | Republican| rowspan=6 nowrap | Mar 4, 1889 –
Mar 3, 1901| rowspan=3 | Elected in 1889.| rowspan=3 | 4|
|- style="height:2em"| | rowspan=3 | 4| rowspan=3 | Re-elected in 1891.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1895.Lost re-election.| rowspan=3 | 5|
|- style="height:2em"| | rowspan=3 | 5| rowspan=3 | Re-elected in 1897.[1] | rowspan=3 | Silver Republican
|- style="height:2em"|
|- style="height:2em"! rowspan=3 | 6| rowspan=3 align=left |
Thomas M. Patterson| rowspan=3 | Democratic| rowspan=3 nowrap | Mar 4, 1901 –
Mar 3, 1907| rowspan=3 | Elected in 1901.Retired.| rowspan=3 | 6|
|- style="height:2em"| | rowspan=3 | 6| rowspan=3 | Re-elected in 1903.Retired.| rowspan=3 | Democratic
|- style="height:2em"|
|- style="height:2em"! rowspan=5 | 7| rowspan=5 align=left |
Simon Guggenheim| rowspan=5 | Republican| rowspan=5 nowrap | Mar 4, 1907 –
Mar 3, 1913| rowspan=5 | Elected in 1907.Retired.| rowspan=5 | 7|
|- style="height:2em"| rowspan=2 | rowspan=5 | 7| Elected in 1909.Died.| nowrap | Mar 4, 1909 –
Jan 11, 1911| | Democratic| align=right |
Charles J. Hughes Jr.! 4
|- style="height:2em"| rowspan=2 | | rowspan=2 nowrap | Jan 11, 1911 –
Jan 15, 1913| rowspan=2 colspan=3 | Vacant
|- style="height:2em"| rowspan=2
|- style="height:2em"| rowspan=2 | Elected to finish Hughes's term.| rowspan=5 nowrap | Jan 15, 1913 –
Mar 3, 1921| rowspan=5 | Democratic| rowspan=5 align=right |
Charles S. Thomas! rowspan=5 | 5
|- style="height:2em"! rowspan=3 | 8| rowspan=3 align=left |
John F. Shafroth| rowspan=3 | Democratic| rowspan=3 nowrap | Mar 4, 1913 –
Mar 3, 1919| rowspan=3 | Elected in 1913.Lost re-election.| rowspan=3 | 8|
|- style="height:2em"| | rowspan=3 | 8| rowspan=3 | Re-elected in 1914.Lost re-election.
|- style="height:2em"|
|- style="height:2em"! rowspan=9 | 9| rowspan=9 align=left |
Lawrence C. Phipps| rowspan=9 | Republican| rowspan=9 nowrap | Mar 4, 1919 –
Mar 3, 1931| rowspan=6 | Elected in 1918.| rowspan=6 | 9|
|- style="height:2em"| | rowspan=6 | 9| rowspan=2 | Elected in 1920.Died.| rowspan=2 nowrap | Mar 4, 1921 –
Mar 24, 1923| rowspan=2 | Republican| rowspan=2 align=right |
Samuel D. Nicholson! rowspan=2 | 6
|- style="height:2em"| rowspan=4
|- style="height:2em"| | nowrap | Mar 24, 1923 –
May 17, 1923| colspan=3 | Vacant
|- style="height:2em"| Appointed to continue Nicholson's term.Retired.| nowrap | May 17, 1923 –
Nov 30, 1924| | Democratic| align=right |
Alva B. Adams! 7
|- style="height:2em"| rowspan=2 | Elected to finish Nicholson's term.Lost renomination.| rowspan=2 nowrap | Dec 1, 1924 –
Mar 3, 1927| rowspan=2 | Republican| rowspan=2 align=right |
Rice W. Means! rowspan=2 | 8
|- style="height:2em"| rowspan=3 | Re-elected in 1924.Retired.| rowspan=3 | 10|
|- style="height:2em"| | rowspan=6 | 10| rowspan=3 | Elected in 1926.Died.| rowspan=3 nowrap | Mar 4, 1927 –
Aug 27, 1932| rowspan=3 | Republican| rowspan=3 align=right |
Charles W. Waterman! rowspan=3 | 9
|- style="height:2em"|
|- style="height:2em"! rowspan=6 | 10| rowspan=6 align=left |
Edward P. Costigan| rowspan=6 | Democratic| rowspan=6 nowrap | Mar 4, 1931 –
Jan 3, 1937| rowspan=6 | Elected in 1930.Retired.| rowspan=6 | 11| rowspan=4
|- style="height:2em"| | nowrap | Aug 27, 1932 –
Sep 26, 1932| colspan=3 | Vacant
|- style="height:2em"| Appointed to continue Waterman's term.Lost election to finish Waterman's term.| nowrap | Sep 26, 1932 –
Dec 6, 1932| | Democratic| align=right |
Walter Walker! 10
|- style="height:2em"| Elected to finish Waterman's term.Lost election to next term.| nowrap | Dec 7, 1932 –
Mar 3, 1933| | Republican| align=right |
Karl C. Schuyler! 11
|- style="height:2em"| | rowspan=3 | 11| rowspan=3 | Elected in 1932.| rowspan=5 nowrap | Mar 4, 1933 –
Dec 1, 1941| rowspan=5 | Democratic| rowspan=5 align=right |
Alva B. Adams! rowspan=5 | 12
|- style="height:2em"|
|- style="height:2em"! rowspan=11 | 11| rowspan=11 align=left |
Edwin C. Johnson| rowspan=11 | Democratic| rowspan=11 nowrap | Jan 3, 1937 –
Jan 3, 1955| rowspan=5 | Elected in 1936.| rowspan=5 | 12|
|- style="height:2em"| | rowspan=5 | 12| rowspan=2 | Re-elected in 1938.Died.
|- style="height:2em"| rowspan=3
|- style="height:2em"| | nowrap | Dec 1, 1941 –
Dec 20, 1941| colspan=3 | Vacant
|- style="height:2em"| rowspan=2 | Appointed to continue Adams's term.Elected in 1942 to finish Adams's term.| rowspan=8 nowrap | Dec 20, 1941 –
Jan 3, 1957| rowspan=8 | Republican| rowspan=8 align=right |
Eugene Millikin! rowspan=8 | 13
|- style="height:2em"| rowspan=3 | Re-elected in 1942.| rowspan=3 | 13|
|- style="height:2em"| | rowspan=3 | 13| rowspan=3 | Re-elected in 1944.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1948.Retired to run for Governor.| rowspan=3 | 14|
|- style="height:2em"| | rowspan=3 | 14| rowspan=3 | Re-elected in 1950.Retired
|- style="height:2em"|
|- style="height:2em"! rowspan=9 | 12| rowspan=9 align=left |
Gordon Allott| rowspan=9 | Republican| rowspan=9 nowrap | Jan 3, 1955 –
Jan 3, 1973| rowspan=3 | Elected in 1954.| rowspan=3 | 15|
|- style="height:2em"| | rowspan=3 | 15| rowspan=3 | Elected in 1956.Lost re-election.| rowspan=3 nowrap | Jan 3, 1957 –
Jan 3, 1963| rowspan=3 | Democratic| rowspan=3 align=right |
John A. Carroll! rowspan=3 | 14
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1960.| rowspan=3 | 16|
|- style="height:2em"| | rowspan=3 | 16| rowspan=3 | Elected in 1962.| rowspan=6 nowrap | Jan 3, 1963 –
Jan 3, 1975| rowspan=6 | Republican| rowspan=6 align=right |
Peter H. Dominick! rowspan=6 | 15
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1966.Lost re-election.| rowspan=3 | 17|
|- style="height:2em"| | rowspan=3 | 17| rowspan=3 | Re-elected in 1968.Lost re-election.
|- style="height:2em"|
|- style="height:2em"! rowspan=3 | 13| rowspan=3 align=left |
Floyd Haskell| rowspan=3 | Democratic| rowspan=3 nowrap | Jan 3, 1973 –
Jan 3, 1979| rowspan=3 | Elected in 1972.Lost re-election.| rowspan=3 | 18|
|- style="height:2em"| | rowspan=3 | 18| rowspan=3 | Elected in 1974.| rowspan=6 nowrap | Jan 3, 1975 –
Jan 3, 1987| rowspan=6 | Democratic| rowspan=6 align=right |
Gary Hart! rowspan=6 | 16
|- style="height:2em"|
|- style="height:2em"! rowspan=6 | 14| rowspan=6 align=left |
William L. Armstrong| rowspan=6 | Republican| rowspan=6 nowrap | Jan 3, 1979 –
Jan 3, 1991| rowspan=3 | Elected in 1978.| rowspan=3 | 19|
|- style="height:2em"| | rowspan=3 | 19| rowspan=3 | Re-elected in 1980.Retired.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 1984.Retired.| rowspan=3 | 20|
|- style="height:2em"| | rowspan=3 | 20| rowspan=3 | Elected in 1986.Retired.| rowspan=3 nowrap | Jan 3, 1987 –
Jan 3, 1993| rowspan=3 | Democratic| rowspan=3 align=right |
Tim Wirth! rowspan=3 | 17
|- style="height:2em"|
|- style="height:2em"! rowspan=4 | 15| rowspan=4 align=left |
Hank Brown| rowspan=4 | Republican| rowspan=4 nowrap | Jan 3, 1991 –
Jan 3, 1997| rowspan=4 | Elected in 1990.Retired.| rowspan=4 | 21|
|- style="height:2em"| | rowspan=4 | 21| rowspan=4 | Elected in 1992.Changed parties on March 3, 1995.| rowspan=7 nowrap | Jan 3, 1993 –
Jan 3, 2005| rowspan=2 | Democratic| rowspan=7 align=right |
Ben Nighthorse Campbell! rowspan=7 | 18
|- style="height:2em"| rowspan=2
|- style="height:2em"| rowspan=5 | Republican
|- style="height:2em"! rowspan=6 | 16| rowspan=6 align=left |
Wayne Allard| rowspan=6 | Republican| rowspan=6 nowrap | Jan 3, 1997 –
Jan 3, 2009| rowspan=3 | Elected in 1996.| rowspan=3 | 22|
|- style="height:2em"| | rowspan=3 | 22| rowspan=3 | Re-elected in 1998.Retired.
|- style="height:2em"|
|- style="height:2em"| rowspan=3 | Re-elected in 2002.Retired.| rowspan=3 | 23|
|- style="height:2em"| | rowspan=4 | 23| rowspan=3 | Elected in 2004.Resigned to become U.S. Secretary of the Interior.| rowspan=3 nowrap | Jan 3, 2005 –
Jan 20, 2009| rowspan=3 | Democratic| rowspan=3 align=right |
Ken Salazar! rowspan=3 | 19
|- style="height:2em"|
|- style="height:2em"! rowspan=4 | 17| rowspan=4 align=left |
Mark Udall| rowspan=4 | Democratic| rowspan=4 nowrap | Jan 3, 2009 –
Jan 3, 2015| rowspan=4 | Elected in 2008.Lost re-election.| rowspan=4 | 24| rowspan=2
|- style="height:2em"| Appointed to finish Salazar's term.| rowspan=10 nowrap | Jan 21, 2009 –
present| rowspan=10 | Democratic| rowspan=10 align=right |
Michael Bennet! rowspan=10 | 20
|- style="height:2em"| | rowspan=3 | 24| rowspan=3 | Elected to a full term in 2010.
|- style="height:2em"|
|- style="height:2em"! rowspan=3 | 18| rowspan=3 align=left |
Cory Gardner| rowspan=3 | Republican| rowspan=3 nowrap | Jan 3, 2015 –
Jan 3, 2021| rowspan=3 | Elected in 2014.Lost re-election.| rowspan=3 | 25|
|- style="height:2em"| | rowspan=3 | 25| rowspan=3 | Re-elected in 2016.
|- style="height:2em"|
|- style="height:2em"! rowspan=3 | 19| rowspan=3 align=left |
John Hickenlooper| rowspan=3 | Democratic| rowspan=3 nowrap | Jan 3, 2021 –
present| rowspan=3 | Elected in 2020.| rowspan=3 | 26|
|- style="height:2em"| | rowspan=3 |26| rowspan=3 | Re-elected in 2022.
|- style="height:2em"|
|- style="height:2em"| rowspan=2 colspan=5 | To be determined in the 2026 election.| rowspan=2 | 27|
|- style="height:2em"| | 27| colspan=5 | To be determined in the 2028 election.