The Corydon Historic District is a national historic district located in Corydon, Indiana, United States. The town of Corydon is also known as Indiana's First State Capital and as Historic Corydon. The district was added to the National Register of Historic Places in 1973, but the listing was amended in 1988 to expand the district's geographical boundaries and include additional sites. The district includes numerous historical structures, most notably the Old Capitol (Indiana's first state capitol building), the Old Treasury Building (Indiana's first state office building), Governor Hendricks' Headquarters, the Constitution Elm Memorial, the Posey House, the Kintner-McGrain House (Cedar Glade), and The Kintner House Inn, as well as other residential and commercial sites.

Corydon, Indiana, which was platted in 1808, continues to serve as the county seat of government for Harrison County, Indiana. The town served as the second capital of the Indiana Territory from 1813 to 1816, but it is best known for its service as the first capital of Indiana from 1816 to 1825. Some of the most significant structures within the historic district date from this early period of the town's history, including the Old Capitol, the centerpiece of the district.

Corydon became the seat of government for the Indiana Territory when the territorial capital was moved from Vincennes, in Knox County, shortly after the outbreak of the War of 1812. Dennis Pennington, a Harrison County representative and the speaker of the territorial legislature's lower house, helped secure Corydon's selection as the capital by pointing out that the Harrison County Courthouse, which the county government planned to build on Corydon's public square, could be used as an assembly building for the territorial legislature. Pennington was awarded the contract to supervise construction of the courthouse, which became known as the Old Capitol.

In addition to its role as the capitol of the Indiana Territory, Corydon served as the site of a constitutional convention to consider statehood for Indiana in 1816. Forty-three delegates convened from June 10 to 29, 1816, to draft Indiana's first state constitution. Sources disagree on the exact location of the gathering. Because the courthouse was not completed at that time, the delegates met at "the courthouse on the hill," which may have referred to a nearby log home that the territorial government had rented. Cramped conditions and the summer heat caused the men to gather under a giant elm tree, which was later named the Constitution Elm. The town's historic district includes a portion of the tree's preserved trunk, surrounded by a sandstone memorial.

The Indiana General Assembly met for the first time at Corydon under the new constitution and state government on November 4, 1816, and Indiana was admitted as the nineteenth state in the Union on December 11, 1816. Corydon served as the first state capital of Indiana from 1816 to 1825, when the seat of state government was moved to Indianapolis. When the historic district was first added to the National Register of Historic Places in 1973, the area encompassed eight sites that existed when Corydon became the capital of Indiana in 1816. These include the Old Capitol building (Harrison County Courthouse), along with the public square surrounding it, Indiana's first state office building (also known as the Old Treasury Building), Governor William Hendricks' Headquarters, the Constitution Elm, the Posey House, the Westfall House, the Branham home/tavern, and the Kintner-McGrain House (named Cedar Glade).

In 1989 the district was extended to Indian Creek in the north and west, east to College Avenue, and south to Little Indian Creek to include additional historic structures. The district's period of significance spans from 1808 to 1929. The district's boundary increase encompassed the eight structures from its early era as a territorial and state capital, as well as commercial and residential buildings constructed after 1825, including a new, three-story county Harrison County Courthouse that was completed in 1929.

A historical marker erected on the Harrison County Courthouse lawn denotes the town's surrender to Confederate Brigadier General John Hunt Morgan's raiders following the Battle of Corydon on July 9, 1863. The battle site, which is located outside of town, is listed separately on the National Register. The district's courthouse square also includes a memorial to the late Indiana governor Frank O'Bannon; his father, Robert P. O'cannon; and grandfather, Lew O'cannon, all of whom were prominent in Corydon. Plans for the O'Bannon memorial on the southwest corner of the courthouse square were announced on May 22, 2007. It includes a lifesize bronze statue of Frank O'Bannon sitting on a limestone bench and three pillars honoring the O'Bannons. The memorial, which cost $200,000, was dedicated in June 2008. Because of its history as a territorial and state capital, Corydon sees an estimated 30,000 visitors each year.

The Old Capitol building, a part of the Corydon Capitol State Historic Site, is administered by the Indiana State Museum and Historic Sites. The two-story, Federal-style, limestone building served as Indiana's first state capitol from 1816 until 1825. The building was originally intended to serve as the Harrison County Courthouse. Construction began in 1814, when Corydon was the capital of the Indiana Territory. The building was nearly completed in 1816, the year that Indiana was granted statehood and its first state legislature convened at Corydon. The building was primarily used as an assembly building for the territorial and state legislatures, but the county government and district courts occasionally used it when the Indiana General Assembly was not in session. Dennis Pennington, who became the state's first speaker of the Indiana Senate after statehood in 1816, supervised its construction.