You really don't have to do anything or you can simply call the sheriff's office and ask if they have something for you to pick up. This is likely a civil suit of some kind for some bill that is owning or some other civil matter.If you haven't committed any crimes or are a possible witness in an ongoing case I would have to say that this is likely some civil court matter.
If you don't call the sheriff you will have to wait until they visit again to find out what this involves.
