Iowa was admitted to the Union on December 28, 1846, and elects United States senators to class 2 and class 3. The state's current U.S. senators are Republicans Chuck Grassley (serving since 1981) and Joni Ernst (serving since 2015). Chuck Grassley is Iowa's longest-serving senator (since 1981).
List of senators
|- style="height:2em" | rowspan=2 colspan=3 | Vacant | rowspan=2 nowrap | Dec 28, 1846 –Dec 7, 1848 | rowspan=2 | Legislature failed to elect. | rowspan=2 | — | | rowspan=2 | — | rowspan=2 | Legislature failed to elect. | rowspan=2 nowrap | Dec 28, 1846 –Dec 7, 1848 | rowspan=2 colspan=3 | Vacant
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|- style="height:2em" ! rowspan=9 | 1 | rowspan=9 align=left | George W. Jones | rowspan=9 | Democratic | rowspan=9 nowrap | Dec 7, 1848 –Mar 3, 1859 | rowspan=3 | Elected in 1848. | rowspan=3 | 1 | 1 | Elected in 1848. | rowspan=4 nowrap | Dec 7, 1848 –Feb 22, 1855 | rowspan=4 | Democratic | rowspan=4 align=right | Augustus C. Dodge ! rowspan=4 | 1
|- style="height:2em" | | rowspan=4 | 2 | rowspan=3 | Re-elected in 1849.Resigned to become U.S. Minister to Spain, having lost re-election.
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|- style="height:2em" | rowspan=6 | Re-elected in 1852.Lost renomination. | rowspan=6 | 2 | rowspan=2
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| nowrap | Feb 22, 1855 –Mar 3, 1855 | colspan=3 | Vacant
|- style="height:2em" | rowspan=3 | rowspan=5 | 3 | Elected in 1855.Elected invalidated, as the Iowa Senate had not participated in it. | nowrap | Mar 4, 1855 –Jan 5, 1857 | | Free Soil | align=right | James Harlan ! rowspan=8 | 2
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| nowrap | Jan 5, 1857 –Jan 29, 1857 | colspan=2 | Vacant
|- style="height:2em" | rowspan=3 | Re-elected to finish his vacant term. | rowspan=6 nowrap | Jan 29, 1857 –May 15, 1865 | rowspan=6 | Republican | rowspan=6 align=right | James Harlan
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|- style="height:2em" ! rowspan=8 | 2 | rowspan=8 align=left | James W. Grimes | rowspan=8 | Republican | rowspan=8 nowrap | Mar 4, 1859 –Dec 6, 1869 | rowspan=3 | Elected in 1858. | rowspan=3 | 3
|- style="height:2em" | | rowspan=5 | 4 | rowspan=3 |Re-elected in 1860.Resigned to become U.S. Secretary of the Interior.
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|- style="height:2em" | rowspan=5 | Re-elected in 1864.Resigned due to ill health. | rowspan=7 | 4 | rowspan=3
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| nowrap | May 15, 1865 –Jan 13, 1866 | colspan=3 | Vacant
|- style="height:2em" | Elected to finish Harlan's term.Clark, p. 141: Kirkwood 118 votes, John Thompson Stoneman (Democratic) 20Lost nomination for the next term. | nowrap | Jan 13, 1866 –Mar 3, 1867 | | Republican | align=right | Samuel J. Kirkwood ! 3
|- style="height:2em" | | rowspan=5 | 5 | rowspan=5 | Elected in 1866.Clark, p. 141: Harlan 118 votes, Henry Hoffman Trimble (Democratic) 20Lost re-election. | rowspan=5 nowrap | Mar 4, 1867 –Mar 3, 1873 | rowspan=5 | Republican | rowspan=5 align=right | James Harlan ! rowspan=5 | 4
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|- style="height:2em" | colspan=3 | Vacant | nowrap | Dec 6, 1869 –Jan 18, 1870
|- style="height:2em" ! 3 | align=left | James B. Howell | | Republican | nowrap | Jan 18, 1870 –Mar 3, 1871 | Elected to finish Grimes's term.Retired.
|- style="height:2em" ! rowspan=3 | 4 | rowspan=3 align=left | George G. Wright | rowspan=3 | Republican | rowspan=3 nowrap | Mar 4, 1871 –Mar 3, 1877 | rowspan=3 | Elected in 1870.Retired. | rowspan=3 | 5
|- style="height:2em" | | rowspan=3 | 6 | rowspan=3 | Elected in 1872. | rowspan=21 nowrap | Mar 4, 1873 –Aug 4, 1908 | rowspan=21 | Republican | rowspan=21 align=right | William B. Allison ! rowspan=21 | 5
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|- style="height:2em" ! rowspan=3 | 5 | rowspan=3 align=left | Samuel J. Kirkwood | rowspan=3 | Republican | rowspan=3 nowrap | Mar 4, 1877 –Mar 7, 1881 | rowspan=3 | Elected in 1876 or 1877.Resigned to become U.S. Secretary of the Interior. | rowspan=4 | 6
|- style="height:2em" | | rowspan=4 | 7 | rowspan=4 | Re-elected in 1878.Clark, p. 185: Allison 104 votes, Daniel F. Miller 35 votes, E. N. Gates 3 votes.
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|- style="height:2em" ! 6 | align=left | James W. McDill | | Republican | nowrap | Mar 8, 1881 –Mar 3, 1883 | Appointed to continue Kirkwood's term.Elected in 1882 to finish Kirkwood's term.Clark, p. 199: Moses M. Ham and Daniel Campbell lost.Retired.
|- style="height:2em" ! rowspan=6 | 7 | rowspan=6 align=left | James F. Wilson | rowspan=6 | Republican | rowspan=6 nowrap | Mar 4, 1883 –Mar 3, 1895 | rowspan=3 | Elected in 1882.Clark, p. 199: La Vega G. Kinne and Daniel P. Stubbs lost. | rowspan=3 | 7
|- style="height:2em" | | rowspan=3 | 8 | rowspan=3 | Re-elected in 1884.Clark, p. 209: Allison 90 votes, Benton J. Hall 48 votes, David M. Clark 10 votes, La Vega G. Kinne 1 vote.
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|- style="height:2em" | rowspan=3 | Re-elected in 1888.Retired. | rowspan=3 | 8
|- style="height:2em" | | rowspan=3 | 9 | rowspan=3 | Re-elected in 1890.Clark, p. 221: Allison 79 votes, Samuel L. Bestow (Democratic) 63 votes, William Larrabee 8 votes.
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|- style="height:2em" ! rowspan=3 | 8 | rowspan=3 align=left | John H. Gear | rowspan=3 | Republican | rowspan=3 nowrap | Mar 4, 1895 –Jul 14, 1900 | rowspan=3 | Elected in 1894.Clark, p. 234: Gear beat Democrat Horace Boies by votes unknown.Re-elected in 1900,Clark, p. 245: Gear 111 votes, Fred E. White (Democratic) 32 votes. but died. | rowspan=5 | 9
|- style="height:2em" | | rowspan=5 | 10 | rowspan=5 | Re-elected in 1896.Clark, p. 238: Allison 118 votes, Washington Irving Babb (Democratic) 25 votes, Frank Q. Stuart 1 vote.
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|- style="height:2em" | colspan=3 | Vacant | nowrap | Jul 14, 1900 –Aug 22, 1900
|- style="height:2em" ! rowspan=8 | 9 | rowspan=8 align=left | Jonathan P. Dolliver | rowspan=8 | Republican | rowspan=8 nowrap | Aug 22, 1900 –Oct 15, 1910 | Appointed to finish Gear's term.
|- style="height:2em" | rowspan=3 | Appointed to begin the vacant term.Elected in 1902 to finish the vacant term.Clark, p. 247: Dolliver 119 votes, John J. Seerley (Democratic) 20 votes. | rowspan=3 | 10
|- style="height:2em" | | rowspan=5 | 11 | rowspan=3 | Re-elected in 1902.Clark, p. 247: Allison 119 votes, Edward Hankinson Thayer (Democratic) 20 votes.Renominated in 1908 but died before the general election.
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|- style="height:2em" | rowspan=4 | Re-elected in 1907.Died. | rowspan=8 | 11 | rowspan=3
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| nowrap | Aug 4, 1908 –Nov 24, 1908 | colspan=3 | Vacant
|- style="height:2em" | Elected to finish Allison's term. | rowspan=16 nowrap | Nov 24, 1908 –Jul 30, 1926 | rowspan=16 | Republican | rowspan=16 align=right | Albert B. Cummins ! rowspan=16 | 6
|- style="height:2em" | rowspan=3 | rowspan=6 | 12 | rowspan=6 | Re-elected in 1909.
|- style="height:2em" | colspan=3 | Vacant | nowrap | Oct 15, 1910 –Nov 12, 1910
|- style="height:2em" ! rowspan=2 | 10 | rowspan=2 align=left | Lafayette Young | rowspan=2 | Republican | rowspan=2 nowrap | Nov 12, 1910 –Apr 11, 1911 | rowspan=2 | Appointed to continue Dolliver's term.Lost election to finish Dolliver's term.
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|- style="height:2em" ! rowspan=6 | 11 | rowspan=6 align=left | William S. Kenyon | rowspan=6 | Republican | rowspan=6 nowrap | Apr 12, 1911 –Feb 24, 1922 | rowspan=1 | Elected to finish Dolliver's term.
|- style="height:2em" | rowspan=3 | Re-elected in 1913. | rowspan=3 | 12
|- style="height:2em" | | rowspan=3 | 13 | rowspan=3 | Re-elected in 1914.
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|- style="height:2em" | rowspan=2 | Re-elected in 1918.Resigned to become Judge of the U.S. Court of Appeals. | rowspan=5 | 13
|- style="height:2em" | rowspan=3 | rowspan=8 | 14 | rowspan=6 | Re-elected in 1920.Lost renomination, then died.
|- style="height:2em" ! 12 | align=left | Charles A. Rawson | | Republican | nowrap | Feb 24, 1922 –Dec 1, 1922 | Appointed to continue Kenyon's term.Retired when his successor was elected.
|- style="height:2em" ! rowspan=3 | 13 | rowspan=3 align=left | Smith W. Brookhart | rowspan=3 | Republican | rowspan=3 nowrap | Dec 1, 1922 –Apr 12, 1926 | rowspan=2 | Elected to finish Kenyon's term.
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|- style="height:2em" | Re-elected in 1924.Lost election challenge. | rowspan=6 | 14 | rowspan=4
|- style="height:2em" ! rowspan=5 | 14 | rowspan=5 align=left | Daniel F. Steck | rowspan=5 | Democratic | rowspan=5 nowrap | Apr 12, 1926 –Mar 3, 1931 | rowspan=5 | Successfully challenged his predecessor's election.Lost re-election.
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| nowrap | Jul 30, 1926 –Aug 7, 1926 | colspan=3 | Vacant
|- style="height:2em" | Appointed to continue Cummins's term.Elected in 1926 to finish Cummins's term.Retired. | nowrap | Aug 7, 1926 –Mar 3, 1927 | | Republican | align=right | David W. Stewart ! 7
|- style="height:2em" | | rowspan=3 | 15 | rowspan=3 | Elected in 1926.Lost renomination and then lost re-election as an Independent. | rowspan=3 nowrap | Mar 4, 1927 –Mar 3, 1933 | rowspan=3 | Republican | rowspan=3 align=right | Smith W. Brookhart ! rowspan=3 | 8
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|- style="height:2em" ! rowspan=5 | 15 | rowspan=5 align=left | L. J. Dickinson | rowspan=5 | Republican | rowspan=5 nowrap | Mar 4, 1931 –Jan 3, 1937 | rowspan=5 | Elected in 1930.Lost re-election. | rowspan=5 | 15
|- style="height:2em" | | rowspan=5 | 16 | rowspan=2 | Elected in 1932.Died. | rowspan=2 nowrap | Mar 4, 1933 –Jul 16, 1936 | rowspan=2 | Democratic | rowspan=2 align=right | Louis Murphy ! rowspan=2 | 9
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| nowrap | Jul 16, 1936 –Nov 3, 1936 | colspan=3 | Vacant
|- style="height:2em" | rowspan=2 | Elected to finish Murphy's term. | rowspan=5 nowrap | Nov 3, 1936 –Jan 3, 1945 | rowspan=5 | Democratic | rowspan=5 align=right | Guy Gillette ! rowspan=5 | 10
|- style="height:2em" ! rowspan=3 | 16 | rowspan=3 align=left | Clyde L. Herring | rowspan=3 | Democratic | rowspan=3 nowrap | Jan 3, 1937 –Jan 3, 1943 | rowspan=3 | Elected in 1936.Did not take seat until Jan 15, 1937 in order to remain Governor of Iowa.Lost re-election. | rowspan=3 | 16
|- style="height:2em" | | rowspan=3 | 17 | rowspan=3 | Re-elected in 1938.Lost re-election.
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|- style="height:2em" ! rowspan=3 | 17 | rowspan=3 align=left | George A. Wilson | rowspan=3 | Republican | rowspan=3 nowrap | Jan 3, 1943 –Jan 3, 1949 | rowspan=3 | Elected in 1942.Did not take seat until Jan 14, 1943 in order to remain Governor of Iowa.Lost re-election. | rowspan=3 | 17
|- style="height:2em" | | rowspan=3 | 18 | rowspan=3 | Elected in 1944. | rowspan=12 nowrap | Jan 3, 1945 –Jan 3, 1969 | rowspan=12 | Republican | rowspan=12 align=right | Bourke B. Hickenlooper ! rowspan=12 | 11
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|- style="height:2em" ! rowspan=3 | 18 | rowspan=3 align=left | Guy Gillette | rowspan=3 | Democratic | rowspan=3 nowrap | Jan 3, 1949 –Jan 3, 1955 | rowspan=3 | Elected in 1948.Lost re-election. | rowspan=3 | 18
|- style="height:2em" | | rowspan=3 | 19 | rowspan=3 | Re-elected in 1950.
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|- style="height:2em" ! rowspan=3 | 19 | rowspan=3 align=left | Thomas E. Martin | rowspan=3 | Republican | rowspan=3 nowrap | Jan 3, 1955 –Jan 3, 1961 | rowspan=3 | Elected in 1954.Retired. | rowspan=3 | 19
|- style="height:2em" | | rowspan=3 | 20 | rowspan=3 | Re-elected in 1956.
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|- style="height:2em" ! rowspan=6 | 20 | rowspan=6 align=left | Jack Miller | rowspan=6 | Republican | rowspan=6 nowrap | Jan 3, 1961 –Jan 3, 1973 | rowspan=3 | Elected in 1960. | rowspan=3 | 20
|- style="height:2em" | | rowspan=3 | 21 | rowspan=3 | Re-elected in 1962Retired.
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|- style="height:2em" | rowspan=3 | Re-elected in 1966.Lost re-election. | rowspan=3 | 21
|- style="height:2em" | | rowspan=3 | 22 | rowspan=3 | Elected in 1968.Retired.