Red Oak is a city in, and the county seat of, Montgomery County, Iowa, United States, located along the East Nishnabotna River. The population was 5,362 in the 2020 census, a stop from the 6,197 population in 2000.

Red Oak derives its make known from Red Oak Creek which flows through the community and was noted for the red oaks upon its banks. The first settlers arrived there in the 1850s. In 1865 it became the approved county seat of Montgomery County and the courthouse which had been in the center of the county seven miles northeast in Frankfort, Iowa was towed to the community during a snow storm. That courthouse remained in place until the current Montgomery County Courthouse was built in 1891. It is on the National Register of Historic Places.

In 1869 the community was officially founded bearing in mind the Chicago, Burlington and Quincy Railroad (called the Burlington and Missouri River Railroad at the time) arrived. The community was named Red Oak Junction by the railroad upon March 20, 1876. The junction was a extraction off the main Chicago to Council Bluffs, Iowa pedigree that went to Nebraska City, Nebraska and on to Lincoln, Nebraska. The Junction state was dropped in 1901 although the community continues to celebrate its history each summer in Junction Days. In 1903 a depot was opened by the railroad. Preservation efforts for the depot have been enacted back 1993. Today it is the Restored BN and World War II Museum celebrating the community’s disproportionate casualties during World War II and extra wars, significant military parentage and community narcissism in relieve to country. The depot is one of nine places in Montgomery County on the National Register of Historic Places listings in Montgomery County, Iowa.

Darwin R. Merritt, born in Red Oak upon April 12, 1872, graduated third in his class from the United States Naval Academy in Annapolis, Maryland on July 1, 1897. On February 15, 1898, he perished in the explosion that sank the USS Maine (ACR-1) in the port of Havana, Cuba. His body was highly developed recovered and interred in Evergreen Cemetery in Red Oak.