With Senate approval of the Louisiana Purchase, the United States acquired over 800,000 square miles of land, extending from the Mississippi River to the Rocky Mountains, including the area forming the present state of South Dakota.
The Dakota Territory, made up of present-day North and South Dakota and parts of Montana and Wyoming, was established by act of Congress.
The U.S. Senate approved the Treaty of Fort Laramie, an agreement between the United States and various bands of the Sioux Nation of Indians.
President Grover Cleveland signed legislation authorizing South Dakota, North Dakota, Montana, and Washington to be organized as states.
President Benjamin Harrison signed the formal proclamation admitting South Dakota as the 40th state in the Union.
Richard F. Pettigrew of Sioux Falls and Gideon C. Moody of Deadwood were seated, becoming South Dakota’s first senators. Two days later they drew lots to determine their Senate class assignments. Pettigrew drew Class 3 (to expire in 1895) while Moody drew Class 2 (to expire in 1891).
James H. Kyle of Aberdeen became chairman of the Senate Committee on Education and Labor (today's Committee on Health, Education, Labor, and Pensions), serving until 1895, and again from 1897 to 1901.
Senator Richard F. Pettigrew left the Republican Party to join the Silver Republican Party. Claiming the Republican Party was "in the hands of trusts and corporations," with a platform authored by "gamblers and shylocks," Pettigrew turned to the newly organized Silver Republicans. Pettigrew failed to win re-election in 1900.
Three party caucuses were held including Republicans, Democrats and Independents. The eight Populists and Silver Republicans meeting as “independent senators” elected Richard Pettigrew to represent them on the Democratic Committee on Committees, as they had agreed to act with the Democratic minority on matters related to Senate organization.
Senator Richard F. Pettigrew delivered a speech criticizing Ohio senator Mark Hanna, accusing him of corruption in winning his Senate seat. Infuriated, Hanna, a powerful party leader close to President William McKinley, then went to South Dakota and successfully campaigned for Pettigrew’s defeat.
The Senate passed an act to authorize the carving of a memorial in the Harney National Forestwhat came to be known as Mt. Rushmore. The president signed the act on March 3, 1925, and work began in 1927.
The Senate Committee on Banking and Currency, chaired by Peter Norbeck, began its investigation of the Wall Street stock market collapse and bank failures. In January 1933, Norbeck appointed former prosecutor Ferdinand Pecora as the committee’s counsel, and the widely publicized hearings of the Pecora investigation led to major reforms of the American financial system.
The Senate accepted a bronze statue of South Dakota educator William Henry Harrison Beadle, sculpted by H. Daniel Webster, as South Dakota's first contribution to the Capitol’s National Statuary Hall Collection. The statue was unveiled on Febraury 23, 1938.
Gladys Pyle of Huron, a member of the state legislature, was elected to complete the unexpired Senate term of Peter Norbeck. Because the Senate did not convene during her short time as South Dakota’s first woman senator, Pyle was never sworn in.
Senator Karl Mundt of Madison chaired the televised Army-McCarthy hearings, when Senator Joseph R. McCarthy was forced to temporarily step aside as chairman of the Senate Permanent Subcommittee on Investigations after he became the subject of its inquiry. The Army-McCarthy hearings continued until June 17.
The Senate passed a concurrent resolution accepting a marble statue of Joseph Ward, educator and author of the South Dakota's constitution, as South Dakota's second contribution to the Capitol’s National Statuary Hall Collection. The unveiling ceremony was held on September 27.
Following the assassination of New York senator Robert F. Kennedy, who had swept the South Dakota primary during his campaign for the Democratic nomination for president, Senator George S. McGovern of Mitchell declared his candidacy for president. At the convention McGovern finished a distant third in the delegate count.
Senator Karl Mundt suffered a paralytic stroke. Although he never returned to the Senate Chamber, Mundt did not resign his seat and served until his term ended on January 3, 1973. With just over 24 years of service, Mundt is South Dakota's longest-serving senator.
By a vote of 55 to 39 the Senate defeated the McGovern-Hatfield Amendment, cosponsored by senators George S. McGovern and Mark Hatfield (R-OR). The much debated amendment would have cut off funding for American participation in the war in Vietnam and required the president to withdraw all U.S. troops by the end of the year. McGovern’s emotional speech to the Senate in favor of the amendment boosted his anticipated presidential campaign in 1972.
Breaking precedent, Senate Republican leaders stripped Karl Mundt of his seniority and his committee assignments. A stroke in 1970 had prevented Mundt from attending the Senate.
Larry Pressler of Humboldt became chairman of the Senate Committee on Commerce, Science and Transportation, serving until 1997.
Former senator George McGovern received the Presidential Medal of Freedom, given by the president of the United States to honor individuals who have made great contributions to either the United States or the world. To date, 24 senators have received the award.
Tom Daschle, who had served as the minority leader since 1995, became the Senate majority leader after Vermont Republican Jim Jeffords joined the Senate Democratic Conference as an independent, thereby giving the Democrats a 51-49 majority. Daschle served as majority leader until 2003, and as minority leader again from 2003 to 2005.
A staff member in the Hart Senate Office Building opened an envelope addressed to Majority Leader Tom Daschle containing a trillion spores of a deadly form of anthrax. Two days later, the building was closed for cleaning and remediation and it did not reopen until January 23, 2002. More than 1,000 members of the Senate, staff, press, lobbyists, and others who passed through the contaminated area on October 15 were screened for anthrax. No one in the Hart Building was sickened by the contamination, but two U.S. postal workers who had handled the contaminated letter died.
Majority Leader Bill Frist (R-TN) traveled to South Dakota to campaign for John Thune, the Republican challenger to Minority Leader Tom Daschle. This appears to have been the first instance of one party floor leader actively campaigning for the defeat of his counterpart.. Daschle lost his bid for reelection.
While participating in a live radio interview with WNAX radio in Yankton, South Dakota, Senator Tim Johnson of Vermillion suffered a brain hemorrhage. He underwent surgery and after a period of recuperation returned to the Senate in September 2007.
The U.S. Senate Commission on Art presented a painting of Senator Tom Daschle at a ceremony in the historic Old Senate Chamber of the U.S. Capitol. The painting is part of the U.S. Senate Leadership Portrait Collection.
Tim Johnson became chairman of the Senate Committee on Banking, Housing, and Urban Affairs.