The 30th United States Congress was a meeting of the legislative branch of the United States federal government, consisting of the United States Senate and the United States House of Representatives. It met in Washington, D.C. from March 4, 1847, to March 4, 1849, during the last two years of the administration of President James K. Polk. The apportionment of seats in the House of Representatives was based on the 1840 United States census. The Senate had a Democratic majority, and the House had a Whig majority. It was the only Congress in which Abraham Lincoln served.

During this congress, two Senate seats were added for the new state of Wisconsin.

During this congress, two House seats were added for the new state of Wisconsin.

This list is arranged by chamber, then by state. Senators are listed by class and representatives are listed by district.

The names of representatives are preceded by their district numbers.

The count below reflects changes from the beginning of the first session of this Congress.

Lists of committees and their party leaders.