Idaho became a state on 3 July 1890. The act of Congress that admitted it carries the line “Approved, July 3, 1890” at its foot, and the Congressional Research Service’s history of statehood records that President Benjamin Harrison signed the bill, H.R. 4562 of the 51st Congress, that day, admitting Idaho as the 43rd state. The Idaho Capitol Commission gives the same date and the same number.
The act itself
The law is chapter 656 of the first session of the 51st Congress, “An act to provide for the admission of the State of Idaho into the Union.” Its first section declares Idaho a state and admits it “on an equal footing with the original States in all respects whatever,” and accepts the constitution Idahoans had written for themselves. Section 3 gave the new state a single Representative in the U.S. House until the next general census. Section 15 appropriated $28,000 to pay for the constitutional convention and the elections around it — money the territory had never had.
Representative Isaac S. Struble of Iowa introduced the bill on 13 January 1890. The House passed it 129 to 1 on 3 April, the Senate passed it without a recorded vote on 1 July, and Harrison signed it two days later.
From territory to state, 1863 to 1890
Congress created Idaho Territory with “An Act to provide a temporary Government for the Territory of Idaho”, printed in the statute book under the date 3 March 1863. The Idaho State Historical Society notes that President Abraham Lincoln did not actually sign it until early on 4 March; acts approved on the last legislative day of an expiring Congress were customarily dated to that day to avoid doubt about their validity.
The territory it created was far larger than the state. It took in all of present Montana and nearly all of Wyoming. Congress cut Montana away on 26 May 1864 and Wyoming on 25 July 1868, and those 1868 lines became permanent when Idaho became a state.
The 1889 convention and the ratification vote
The territorial legislature refused to provide for a constitutional convention, so Governor E. A. Stevenson called one on his own initiative on 2 April 1889, with no money for delegate elections or for a ratification vote. Delegates met in Boise on 4 July 1889 and voted 51 to 0 to adopt a constitution on 6 August. Voters ratified it on 5 November 1889 by 12,398 to 1,773. The admission act’s preamble recites both steps, dating the convention’s work to 4 July 1889 and the ratification election to the first Tuesday in November that year. The full account of the reasons behind all this is on why Idaho became a state.
Where Idaho sits in the run of admissions
Six states entered the Union in a little over eight months. North Dakota and South Dakota were admitted on 2 November 1889, Montana on 8 November, Washington on 11 November, Idaho on 3 July 1890 and Wyoming on 10 July 1890. Those first four came in under an enabling act President Grover Cleveland signed on 22 February 1889; Idaho and Wyoming were not in it, and each was admitted by its own separate act a year and a half later. Idaho’s place in the sequence sets out the whole run with dates.