Green Castle, also spelled Greencastle, is an unincorporated community in Jasper County, in the U.S. state of Iowa.

Green Castle lies along the junction of North 51st Avenue W and West 112th Street N, a half mile west of Iowa Highway 117.

[1] Greencastle was platted in Section 16 of Powesheik Township.

A school was built there in 1849, a flour mill followed in 1875, and in 1878 15 buildings were constructed in Greencastle.

[2] The Greencastle post office opened in August 1856 and closed in December 1901.