C# code for creating Folders within SharePoint List Programmatically

using (SPSite oSPsite = new SPSite("http://MyWebSiteURLHere"))

{

    oSPsite.AllowUnsafeUpdates = true;

    using (SPWeb oSPWeb = oSPsite.OpenWeb())

    {

        oSPWeb.AllowUnsafeUpdates = true;

        /* Path within the list where the new folder gets created

           Leave it empty if it needs to be created under root */

        String nodeDepthPath = @"/MyRootFolder";

        /* get the list instance by name */

        SPList list = oSPWeb.Lists["List_Name"];

        /* create a folder under the path specified */

        SPListItem folderItem = list.Items.Add(

            list.RootFolder.ServerRelativeUrl + nodeDepthPath,

            SPFileSystemObjectType.Folder);

                   

        /* set the folder name and update */

        folderItem["Title"] = "New_Folder_Name";

        folderItem.Update();

        oSPWeb.AllowUnsafeUpdates = false;

    }

    oSPsite.AllowUnsafeUpdates = false;

}