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Below I am pasting an email from a historian, whom I asked about the correct title.| talk  

The truth is that the English language really has no equivalent to Freiherr (the title of the ruler) or Freiherrschaft (the title of the political entity), because neither or them existed in the English-speaking world.  The loose translations sometimes given (baron, barony) are inaccurate, in that they do not convey the concept of independent jurisdiction.  Medieval English barons were juridically much more subject to the kings than these (except for the few exceptions such as the liberty of the bishops of Durham and a few other historical exotica).
The concept wasn't limited to Silesia.  It existed throughout the Holy Roman Empire and within the hereditary domains of the Habsburgs, such as Bohemia after 1621.
It is normally preferable to keep the German term, italicized, and give a sentence or so of explanation."