The Five Towns eruv is contiguous to the Far Rockaway eruv, so I'll assume that the Techum of Far Rockaway extends through the Five Towns. The shortest straight-line distance between the closest points of the borders of the Five Towns and West Hempstead eruvim is, according to Google, almost exactly 3km or 9700 feet. Techum Shabbos is 2000 amot, which is approximately 1km, thus placing West Hempstead significantly past the techum.
However, according to the Orthodox Union,
According to this, you would be able to freely walk from Far Rockaway well into Suffolk County before leaving the techum.
Disclaimer: I'm not an expert of eruvin or techum shabbos, and I may be going about this all wrong. CYLOR.