According to the Book of Joshua, Eglon was a Canaanite city, whose king Debir joined a confederacy against Gibeon when that city made peace with Israel. The five kings involved were slain and Eglon was later conquered and its inhabitants condemned to destruction. It was thereafter included in the territory of the Tribe of Judah, although it is not mentioned outside of the book of Joshua. According to K. Van Bekkum, the location of Eglon is unknown, but the most plausible candidate is Tel Eiton. The ancient name is preserved at the ruins of Khirbet Ajlan, a few km distant.
According to Carl S. Ehrlick, "the overwhelming consensus of modern scholarship is that the conquest tradition of Joshua is a pious fiction."
References
Eglon, Canaan Wikipedia(Text) CC BY-SA