The New Castle Archaeological Site, also designated as Indiana archaeological site 12-Hn-1, is a highly significant Middle Woodland period earthwork and mound complex located near the Blue River in Henry County, Indiana. Attributed primarily to the Hopewell culture with earlier Adena influences, the site dates from approximately 100 B.C. to A.D. 400 and originally comprised a diverse group of earthworks, including circular enclosures, embankments, and several burial mounds. Situated on the grounds of what later became the New Castle State Developmental Center, this prehistoric complex represents one of the major ceremonial and mortuary centers in the upper West Fork of the White River drainage system, illustrating the complex social structures, engineering capabilities, and ritual practices of the region's ancient inhabitants.

The site's archaeological significance was firmly established through systematic excavations conducted in the late 1960s and early 1970s by Ball State University under the direction of archaeologist B.K. Swartz Jr. These investigations uncovered a wealth of diagnostic artifacts and structural features, including cremated and bundle burials, ceremonial copper objects, exotic mica, unique pottery sherds, and diagnostic lithic tools. The presence of these high-status grave goods and non-local materials demonstrates the site's integration into the vast Hopewell Interaction Sphere, a prehistoric trade network that spanned much of eastern North America. Listed on the National Register of Historic Places in 1976, the New Castle Archaeological Site remains a critical resource for understanding Woodland-era population dynamics, ceremonial behaviors, and regional trade in East-Central Indiana.