Iowa entered the Union as the nation's 29th state during the 29th Congress, but the state legislature did not elect senators to that Congress.
Long-time friends George W. Jones of Dubuque and Augustus Caesar Dodge of Burlington presented their credentials and were sworn into office as Iowa's first two United States senators. The senators then drew lots to determine their class assignments. Augustus Dodge drew Class 1, with a term to expire March 3, 1849. George Jones drew Class 3, with a term to expire March 3, 1853. Augustus Dodge's father, Henry Dodge, served at that time as one of Wisconsin's two senators. The Dodges are the only father and son to have served simultaneously in the Senate.
The Democratic-controlled Senate resolved the contested 1855 election in Iowa of Republican James Harlan of Mount Pleasant by declaring the seat vacant. The Senate had permitted Harlan to serve during the 13 months it took to resolve the case. Five days after the Senate's action, the Iowa legislature reelected Harlan and the Senate seated him.
The Senate voted on articles of impeachment against President Andrew Johnson. The vote was one short of the two-thirds margin required for removal. Senator James W. Grimes of Burlington, stricken with paralysis, was carried to the chamber to vote "not guilty"—one of only seven Radical Republicans to do so. Their votes kept Johnson in office. Senator James Harlan voted for conviction.
William B. Allison of Dubuque began what would become a 35-year Senate career.
William B. Allison was elected Republican Conference chairman, a position he held until 1908. Allison was among the group of four power brokers (including Orville Platt, Nelson Aldrich, and John Spooner), known as the "Senate Four," who largely controlled Senate legislative operations between 1897 and 1905.
Jonathan P. Dolliver of Fort Dodge became chairman of the Senate Committee on Education and Labor (today's Committee on Health, Education, Labor, and Pensions), serving until 1909.
Senator William B. Allison died. At the time of his death, he had served in the Senate for 35 years and 5 months. This established him as the second longest-serving senator in history to that time (Francis E. Warren of Wyoming had served 37 years), the longest-serving Iowa senator to date, and the longest-serving Senate committee chairman (24 years).
The Senate purchased an existing oil portrait of the late senator William B. Allison by artist Wilbur Reaser. The portrait is displayed in a place of honor at the south entrance to the Senate Chamber.
A bronze statue by artist Nellie V. Walker of former senator James Harlan was placed in the Capitol as Iowa's first contribution to the National Statuary Hall Collection. Harlan served in the Senate from 1855 to 1865 and again from 1867 to 1873. Harlan's statue was replaced by one of Norman Borlaug in 2014.
The Seventeenth Amendment to the U.S. Constitution took effect allowing for the direct election of U.S. senators. Senator Albert B. Cummins, a member since 1908, became Iowa's first popularly elected senator on November 3, 1914. As governor, Cummins had secured passage of a 1907 direct primary law for Iowa's senatorial elections.
A bronze statue of Senator Samuel Jordan Kirkwood of Iowa City was placed in the Capitol as Iowa's second entry in the National Statuary Hall Collection. Kirkwood served in the Senate from 1866 to 1867 and again from 1877 to 1881. The sculptor was Vinnie Ream, who at age 16 earned national fame by creating the Capitol's statue of President Abraham Lincoln.
Albert B. Cummins was elected president pro tempore of the Senate. He held that post until 1925. In 1910 a journalist described him as follows: "Suave, skillful, faultless in designing, in exposition faultless; never bitter, never once losing control; stocked with merciless information that crushed all attempts to befog the issues, Cummins worked out a pattern of constructive statesmanship that amazed the close watchers of governmental affairs in Washington." Cummins died in office in 1926.
William S. Kenyon became chairman of the Senate Committee on Education and Labor (today's Committee on Health, Education, Labor, and Pensions), serving until 1922.
After a month-long delay, the Senate resolved the 1924 contested election in Iowa between Daniel F. Steck and Smith W. Brookhart. Steck of Ottumwa was seated. Brookhart of Washington was the first senator unseated after a recount. He subsequently won election later in 1926 and served until 1933. He lost the elections of 1932 and 1936.
Henry A. Wallace of Orient was sworn into office and began presiding over the Senate as the 33rd vice president of the United States. Wallace, a former secretary of agriculture in President Franklin D. Roosevelt's cabinet, served as vice president until 1945.
A marble portrait bust of Vice President Henry A. Wallace by artist Jo Davidson, one of the best-known American portrait sculptors of early 20th century, was placed in Senate wing of the Capitol. Part of the Senate Vice Presidential Bust Collection, the sculpture had been completed in 1947. Renovations to the Capitol's interior delayed the public display of the bust.
Richard C. Clark of Marion, administrative assistant to Representative John C. Culver of Cedar Rapids, won election to the Senate. Two years later, Culver won Iowa's other Senate seat, thereby becoming junior in the Senate to his former employee.
Thomas R. Harkin of Cumming became chairman of the Senate Committee on Agriculture, Nutrition, and Forestry. He served as ranking member from 2003 to 2007, and became chairman again from 2007 to 2009. In 2009 he became chairman of the Senate Committee on Health, Education, Labor, and Pensions.
Charles E. Grassley of New Hartford became chairman of the Senate Committee on Finance. He served briefly in 2001, from January 20 to June 6 (when Vermont Republican James Jeffords became an Independent and began caucusing with the Democrats, giving Democrats control of the Senate), and returned as chairman from 2003 to 2007.