While configuring SharePoint 2013 Search service, we have the option to change the SharePoint search index location. If we don’t change it during configuration, it is configured to use default location, which is
C:\Program Files\Microsoft Office Servers\15.0\Data
If you have already changed your index location during or after configuration and need to find that, you can use the following PowerShell commands.
$searchInstance = Get-SPenterpriseSearchServiceInstance
this gives you the IndexLocation.
For many reasons, we don’t want our C drive space to be filled up with Index. At some point, with all the updates, we may run short of space. If you would want to change/move the index location there are many useful step by step explainations out there. I had success using this one before.