1846 and 1847 United States House of Representatives elections
Elections to the United States House of Representatives for the 30th Congress were held during President James K. Polk's term at various dates in different states from August 1846 to November 1847.
The Whigs gained 37 seats to win 116 and a change in partisan control, while the rival Democrats lost 30, falling to 112. The Whigs gained seats in the Mid-Atlantic and the South. The nativist and anti-Catholic American Party was reduced to one seat. One Independent, Amos Tuck, was elected from New Hampshire.
The Mexican–American War was the main issue before voters. The incumbent House had voted overwhelmingly for war, but Polk had won the Presidency only by plurality in 1844 over his more famous opponent Henry Clay. Voters west of the Appalachian Mountains enthusiastically supported war, but voters in northeastern, more urban regions widely opposed it.
It was widely, accurately believed that war with Mexico would be won and would include large territorial gains. The Wilmot Proviso was the first Congressional attempt to deal with the political question of slavery in these projected new territories, by proposing to ban it. Congress rejected the Wilmot Proviso, but not quickly or smoothly. Protracted debate highlighted the issue, aggravating sectional tensions. The repeated failure of Congress, and later also the President and Supreme Court, over the next decade to resolve this issue conclusively was a major cause of the Civil War.
Notable freshmen included Abraham Lincoln, elected as a Whig to his only term. This was the last time the Whig Party won a House majority, though candidates opposed to the Democratic Party would win a large majority in the realigning 1854 election.
Election summaries
The trend toward single-member districts culminated as no multi-member districts featured.In 1845, Congress established a uniform date for choosing Presidential electors. Gradually, states aligned nearly all other elections with this date, though as of this election, only three states had done so.
Two seats were added for the new State of Wisconsin. Wisconsin was unrepresented for most of the 1st session.
Special elections
Florida
Wisconsin
Wisconsin was admitted to the union in 1848 and elected two representatives to the 30th congress on May 8, 1848.Non-voting delegates
| District | Incumbent | Party | First elected | Result | Candidates |
| Morgan Lewis Martin | Democratic | 1844 | Incumbent was not renominated. New member elected. Whig gain. |