Green Mountain is a rural unincorporated community and census-designated place (CDP) in Marshall County, Iowa, United States.

The present-day town of Green Mountain, south of the original townsite, was established in 1883, platted by the Iowa Construction Company.

The town was built adjacent to the Chicago Great Western Railroad.

The wreck is known as the worst ever in Iowa history, as 52 people were killed in the accident on March 21, 1910.

According to the U.S. Census Bureau, the Green Mountain CDP has an area of 0.69 square miles (1.79 km2), all land.

[1] The headwaters of Nickolson Creek run through the west side of the community, flowing south to join Rock Creek, which in turn joins the Iowa River east of Marshalltown.