"The Platte County Courthouse faces south in the center of the public square at Third and Main Streets in Platte City. It is a classically derived structure, originally cruciform in shape, with a partial basement and unfinished attic. This shape has been modified by a widening and extension of the north wing to create an enlarged facility conceived to meet present day requirements. While this addition has, of necessity, modified the scale of the courthouse, it has done so with a sympathy for the original materials and decorative motifs.
The Platte County Courthouse, Platte City, is a significant example of classically derived architecture of local design, materials and workmanship. It is a valuable symbol of Its city, county and the State of Missouri.
Prior to the construction of a courthouse, the county and circuit courts met in various cabins or stores in the town. In December, 1840, the first Platte County Courthouse was begun, and it was finished a few months later at a total cost of $15,000. Demetrius A. Sutton drew the plans and specifications, for which he received the sum of $10. The courthouse was located on the southeast corner of Block 25. It was a two-story, wooden building, about 50 feet square and surmounted by a cupola, ball and spire.
By 1861, the entire nation was embroiled in the issues which would lead to the Civil War and which would prove disastrous for the twenty-one year old courthouse. The southern states having seceded Missouri elected to remain loyal only after passionate argument. The sentiments of Missourians were deeply divided, especially in Platte City, where, although there was no outward rebellion, southern flags were flying and Union sympathizers ostracized. Platte City was the scene of intense upheaval, with both north and south conducting guerrilla warfare and wreaking havoc on the city and its people." In retaliation to the guerrilla activity, on December 16, 1861, Federalist troops, led by Colonel Morgan, set fire to much of the town, including the courthouse, which was totally destroyed. Fifty years later, the question of whether or not Colonel Morgan deliberately burned the courthouse was still in dispute. In 1905 and again in 1906 the county tried to gain restitution for the burning from the U.S. Court of Claims. Unsuccessful, they sought an appeal from the Supreme Court, but lost there as well.
Although the Civil War's deleterious effects on Platte City and Platte County did not end with the burning of the city in 1861, by 1864 the county was beginning its preparations to rebuild. On April 2, 1864, C.P. Lewis, county clerk, advertised for bids to rebuild the courthouse and jail. It is assumed that county business was conducted elsewhere, but no mention was made of the temporary location. Prisoners were removed to jails in other counties. Before the rebuilding could begin, however, the town was burned once again by the Union Army in retaliation against southern bushwackers operating in the area" The burning of 1864 was for Platte City the last great catastrophe of the war. Soldiers and residents returned and reconstruction began.
In 1865, Joseph Murphy was appointed commissioner of public buildings and $100,000 appropriated for a new courthouse. 11 Block 24 had been purchased by the county as a public square, and this site was chosen for the proposed courthouse and jail. Peter McDuff was selected as architect, and the bid of J.A. McGonagle of $88,500 was accepted. On June 20, 1866, the cornerstone of the present courthouse was laid, and the completed building was dedicated on St. Valentine's Day, 1867 with "...a dance and carousel." - National Register Nomination form