Grasshopper: Where is Grasshopper.dll and GH_IO.dll?

When developing Grasshopper components, we need to make reference to two Grasshopper Dlls: Grasshopper.dll and GH_IO.dll. These provide the GH_Component class, which custom components inherit from, as well as providing other useful Grasshopper functions.

Grasshopper.dll and GH_IO.dll

The exact location depends upon your particular Rhino installation. On my computer, I found them buried within the AppData folder at:

C:\Users\James\AppData\Roaming\McNeel\Rhinoceros\5.0\Plug-ins\Grasshopper {...}\0.9.76.0

Within this folder, I found a large collection of files, including Grasshopper.dll and GH_IO.dll.

A similar path may exist on your computer. If you can’t find anything like it on yours, you can look up the folder through Rhino: (from David Rutten)

1. Start Rhino
2. Run the _PluginManager command
3. Locate Grasshopper in the list of plugins
4. Open the properties for the Grasshopper plugin
5. At the bottom of the Properties window there’s a ‘File name’ entry
6. This points to GrasshopperPlugin.rhp, which is sitting next to Grasshopper.dll

You may need to widen the window to see the full path.