Were there any Shtetlach in pre war Europe that had an Eruv? Which ones?
Many of them in fact had eiruvin. As a side note to a class on Children on Shabbat, Rabbi Tzvi Sobolofsky mentioned that Brisk had one in the days of Rabbi Chaim Soloveitchik. His attitude seemed to be that this was hardly exceptional.
While they hardly qualify as shtetlach, Rabbi Herschel Shachter mentioned that both Warsaw and Paris had eiruvin in the 19th century.
All big towns and shtetls in pre-war Poland had an eruv, if you were to research the towns and hamlets that today lay in the area of what was the pre-war Second Polish RP, you would find that every location even the smallest of villages as small into today's population as a thousand had a functional eruv up until 1939.
(That info was added by an anonymous user, known only by the IP address of the machine he added it from, and that IP address,
126.96.36.199 (in Melbourne), made no other edits to Wikipedia or its sister sites, ever, as far as I can see. He also added no citation to the Wikipedia article for his claim. So I have no way of judging this claim (and no reason to think it's true). But there you have it, for what it's worth.)