Historical marker #1251 in La Grange tells the history of Oldham County. It became a county in 1824, having been formed from parts of Henry, Jefferson, and Shelby Counties, making it the 74th Kentucky County.
The naming of the county is credited to the memory of Lt. Col. William Oldham, a captain in the Revolutionary War. He served the Continental forces until the spring of 1779 when he resigned to move to the Falls of the Ohio. While commanding the Kentucky militia, Lt. Colonel William Oldham was one of over 800 killed in a battle against Native Americans known as "St. Clair's Defeat" on November 4, 1791. Oldham County was created 33 years after his death and is named in his honor. Some family members, including his wife Penelope, are buried in the Churchill family cemetery located in Churchill Park in Louisville. Col. Oldham is buried in a mass grave at Ft. Recovery Monument Park in Ft. Recovery, Mercer Co., OH.
The county seat was first established along the Ohio River in Westport, which became a bustling river city in the early 1800s. The town was chosen as the county seat in 1823 and a courthouse established in what is now the Westport Methodist Church. County leaders finally decided upon a permanent home for the courthouse in La Grange by 1838. Agriculture has played a major role in the county since its founding, but Oldham County is perhaps best known for its thoroughbred horse industry. Many of these farms lie along U.S. 42.
One of the biggest changes in the county may have been when the Louisville and Frankfort Railroad Company introduced rail lines in the area in the 1850s. This forced many new towns and communities to spring up. Eventually the railroad ceased operating as a form of public transportation, but trains still rumble along Main Street through the downtown area daily. The interurban railway played a major part in transportation and the growth of the county as well as the railroad.