If you are trying to build a new hydrologic model, please use (which has a modern GIS interface) instead.
However, many legacy users still need to run it. This post reflects the last known working method for ArcGIS 10.8, but verify the links as USACE changes them frequently. Disclaimer: HEC-GeoHMS is officially retired. The USACE now recommends using HEC-HMS v4.5+ (which has built-in GIS tools) or the new HEC-HMS for QGIS. This guide is for legacy project maintenance only.
