The 1860–61 United States Senate elections were held from January 14, 1860, to April 2, 1861. Regularly scheduled elections were held for 23 out of the 68 seats in the United States Senate, and special elections were held in California, Oregon, Maine, Pennsylvania, and Ohio. One seat was previously elected on December 12, 1859. Following the start of the 37th Congress on July 4, 1861, special elections were held in Virginia and Kentucky to fill vacancies resulting from the secession of the Confederacy. The Republican Party flipped six Democratic-held seats and gained control of the Senate for the first time following the departure of senators representing Confederate states.

U.S. senators are divided into three classes whose six-year terms are staggered, such that one-third of the Senate is elected every two years. Senators in Class 3 were elected in 1860 and 1861. Prior to ratification of the Seventeenth Amendment in 1913, senators were elected by the U.S. state legislatures. There was no fixed calendar, and states held elections on various dates preceding the first session of Congress. In states with split partisan control of the legislature, multiple rounds of voting could be required to elect a senator, leading to extended vacancies.

Republicans flipped Democratic-held seats in Indiana, Ohio, Oregon, and Pennsylvania and added two seats representing the new state of Kansas, swelling their caucus to 31 senators. The Democrats flipped a Know Nothing-held seat in Kentucky, but lost five seats from states that seceded before the end of the 36th Congress; the departure of 16 more Southern senators before July 4 reduced the Democratic caucus to 15 seats. In special elections held after the start of Congress, Unionists filled two vacancies in Virginia and flipped a Democratic-held seat in Kentucky, reducing the Democratic caucus to 14 seats by the end of 1861.

The Republican victory in the 1860 United States presidential election precipitated the resignations of senators Hannibal Hamlin of Maine, Simon Cameron of Pennsylvania, and Salmon P. Chase of Ohio, who became vice president, secretary of war, and secretary of the treasury, respectively, in the incoming Lincoln administration; Republicans won all three special elections to select their replacements. Other notable departures included William H. Seward of New York, who retired in order to accept an appointment as secretary of state; Stephen A. Douglas, who died on June 3, 1861, and was replaced by a Republican appointee; John C. Breckinridge, who was expelled from the Senate in December 1861 after enlisting in the Confederate States Army; and Joseph Lane of Oregon, whose seat was filled by a Douglas Democrat.

Background The elections took place amidst rising sectional tension over slavery and the related issue of territorial expansion. In the previous Congress, the debate on the proposed Lecompton Constitution and the application of the Dred Scott decision split the Democratic Party between allies of Stephen A. Douglas, who opposed the measures, and the administration of James Buchanan. Douglas was nominated for president by his supporters in 1860, while the Buchanan wing consisting of most Southern Democrats and doughfaces coalesced behind the outgoing vice president and senator-elect from Kentucky, John C. Breckinridge. In California, Missouri, and Oregon, vote-splitting between Douglas and Breckinridge Democrats resulted in gridlock that persisted over multiple rounds of balloting. Republicans were the beneficiaries of Democratic infighting, picking up an open seat in Oregon and using their influence to elect a Douglas Democrat over his Breckinridge Democratic opponent in California.

In the slave states, the opposition to the Democrats was fragmented and generally lacked sufficient numbers to threaten Democratic senators. Of the five slave states to hold regularly scheduled elections, only in Missouri was there a protracted struggle over the selection of the state's senator. In Maryland the Know Nothings were the second party in the legislature, and in North Carolina the Whig label was revived; elsewhere the opponents of the Democrats were called Oppositionists or Constitutional Unionists. These groups subsequently would join forces with unionist Democrats and Republicans in Union coalitions that resisted secession in the Upper South and border states during and after 1861.

Summary results Parties Total Democratic Republican Know Nothing Union Vacant Last elections (1858–59) 38 25 2 — 1 66 Not up 23 16 1 — — 40 10 8 1 — — 19 13 8 — — — 21 Up 15 9 1 — 3 28 14 7 1 — — 22 1 2 — — 1 4 — 1 — — — 1 — — — — 2 2 General election 1859 — — 1 — — 1 1 Know Nothing replaced by 1 Democrat 1 1 — — — — 1 1860 5 4 — — — 9 3 4 — — — 7 1 Democrat replaced by 1 Republican 1 Democrat replaced by 1 vacancy 2 3 5 — — 1 9 1861 9 3 — — 2 14 3 3 — — — 6 4 Democrats replaced by 4 vacancies 2 Democrats replaced by 2 Republicans 2 vacancies replaced by 2 Republicans 8 3 7 — — 4 14 Special elections 1860 1 — — — 1 2 1 — — — — 1 1 vacancy replaced by 1 Republican 1 1 1 — — — 2 1861 — 3 — — — 3 — 3 — — — 3 — 3 — — — 3 Secession Before March 4, 1861 9 — — — — 9 9 Democrats replaced by 9 vacancies 9 — — — — 9 9 After March 4, 1861 8 — — — — 8 1 — — — — 1 7 Democrats replaced by 7 vacancies 7 1 — — — 7 8 Result 15 31 1 — 21 68 1 3 2 68

Maps

Change in composition Each block represents one of the 66 seats in the U.S. Senate. (The admission of Kansas on January 29, 1861, increased the number of seats in the Senate to 68.) "KN" is a Know Nothing senator, "D" is a Democratic senator, "R" is a Republican senator, "U" is a Union senator, and "V" is a vacant seat. They are arranged so that the parties are separated, and a majority is clear by crossing the middle.

Before the elections This diagram shows the composition of the Senate on January 1, 1860.

D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D Majority → D R R R KN KN D D D D R R R R R R R R R R R R R R R R R R R R R R V

After the elections This diagram shows the projected composition of the Senate as a result of the regularly scheduled elections for the Class III seats and special elections in California and Oregon. In consequence of secession, several more seats had been vacated by the time the 37th United States Congress convened, as shown below.

D V V V D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D No majority R R R R R R R R R KN R R R R R R R R R R R R R R R R R R R R R R V V

Beginning of the first session This diagram shows the composition of the Senate on July 11, 1861, after the start of the first session, following the withdrawal or expulsion of 16 senators from states which had seceded from the Union between Election Day (November 8, 1860,) and the opening of Congress on July 4. Special elections held in Pennsylvania, Maine, and Ohio filled three vacancies which had occurred on or before March 4; a final vacancy, occurring as a result of the death of Stephen A. Douglas of Illinois, was filled by appointment pending a special election.

V V V V V V V V V V V D D D D D D D D D D D D D D KN R R R R R R R R Majority → R R R R R R R R R R R R R R R R R R R R V V V V V V R R R R V V V V

Beginning of the second session This diagram shows the composition of the Senate on December 10, 1861, after the start of the second session, following special elections held in Kentucky and Virginia to fill vacancies resulting from the expulsion of pro-Confederate senators; a final vacancy, occurring from the death of Edward D. Baker, was filled by appointment pending a special election.

V V V V V V V V V V D D D D D D D D D D D D D D KN U U U R R R R R R Majority → R R R R R R R R R R R R R R R R R R R R V V V V V R R R R R V V V V

Key: KN# Know Nothing D# Democratic R# Republican U# Union V# Vacant

Race summary

Special elections during the preceding Congress Special elections were held between January 14, 1860, and January 9, 1861, to fill three vacancies in the 36th United States Congress.

State Incumbent This race Senator Party Electoralhistory Results Candidates California(Class 1) Henry P. Haun 1859 Interim appointee retired.New member elected January 14, 1860.Democratic hold. First ballot Oregon(Class 2) Vacant (legislature failed to elect) Seat vacant since March 4, 1859.New member elected October 2, 1860.Republican gain. Fourteenth ballot Maine(Class 1) Hannibal Hamlin 1848 18511857 1857 Incumbent resigned January 7, 1861.New member elected January 9, 1861.Republican hold. First ballot

Elections leading to the next Congress Eighteen senators were elected for the term beginning March 4, 1861. State Incumbent This race Senator Party Electoralhistory Results Candidates Alabama Benjamin Fitzpatrick 1848 1849 1853 1853 1855 No election.Democratic loss. None. Arkansas Robert W. Johnson 1853 1854 1855 Incumbent retired.Democratic hold. Ninth ballot California William M. Gwin 18501855 1857 Incumbent retired.Democratic hold. Twenty-third ballot Connecticut Lafayette S. Foster 1854 Incumbent re-elected. First ballot Florida David L. Yulee 1855 No election.Democratic loss. None. Georgia Alfred Iverson 1854–55 No election.Democratic loss. None. Illinois Lyman Trumbull 1855 Incumbent re-elected. First ballot Indiana Graham N. Fitch 1857 Incumbent retired.Republican gain. First ballot Iowa James Harlan 18551857 1857 Incumbent re-elected. First ballot Kansas None (new state) Seat created January 29, 1861.Republican gain. First ballot Seat created January 29, 1861.Republican gain. Kentucky John J. Crittenden Know Nothing 18161819 18351841 1842 1842 18431848 1854 Incumbent retired.Democratic gain. First ballot () Louisiana John Slidell 1853 1854–55 No election.Democratic loss. None. Maryland James Pearce 184318491855 Incumbent re-elected. First ballot Missouri James S. Green 1857 Incumbent withdrew during election.Democratic hold. Fifteenth ballot New Hampshire Daniel Clark 1857 Incumbent re-elected. First ballot New York William H. Seward 18491855 Incumbent retired.Republican hold. First ballot North Carolina Thomas L. Clingman 1858 1858 Incumbent re-elected. First ballot Ohio George E. Pugh 1854 Incumbent lost re-election.Republican gain. First ballot Oregon Joseph Lane 1859 Incumbent retired.Democratic hold. Fourteenth ballot Pennsylvania William Bigler 1856 Incumbent retired.People's gain. First ballot South Carolina James H. Hammond 1857 No election.Democratic loss. None. Vermont Jacob Collamer 1855 Incumbent re-elected. First ballot Wisconsin Charles Durkee 1855 Incumbent retired.Republican hold. First ballot

Special elections during the next Congress

State Incumbent This race Senator Party Electoralhistory Results Candidates Pennsylvania(Class 1) Simon Cameron People's 1857 Incumbent resigned March 4, 1861.New member elected March 14, 1861.People's hold. First ballot Ohio(Class 3) Salmon P. Chase Republican 18491855 1860 Incumbent resigned March 6, 1861.New member elected March 21, 1861.Republican hold. First ballot Virginia(Class 1) James M. Mason Democratic 1847 18501856 Incumbent expelled July 11, 1861.New member elected July 9, 1861.Union gain. First ballot Virginia(Class 2) Robert M. T. Hunter Democratic 184618521858 Incumbent expelled July 11, 1861.New member elected July 9, 1861.Union gain. First ballot Kentucky(Class 3) John C. Breckinridge Democratic 1859 Incumbent expelled December 4, 1861.New member elected December 10, 1861.Union gain. First ballot

Alabama

One-term Democrat Benjamin Fitzpatrick was elected in 1855. He withdrew from the Senate on January 21, 1861, following the secession of Alabama. The Alabama Legislature did not hold an election for the next term, and the seat remained vacant until 1868.

Arkansas

One-term Democrat Robert W. Johnson was elected in 1855. He was not a candidate for re-election.