Treglwang is a former municipality in the district of Liezen, in the Austrian state of Styria. It lies in the mountainous interior of Austria, within the Liezen district, the largest district in Styria by area.
Since the 2015 Styria municipal structural reform, Treglwang is no longer an independent municipality and has been part of the municipality of Gaishorn am See. The reform reduced the number of municipalities in Styria through mergers, and Treglwang was among those absorbed into a neighbouring community.
As a result, Treglwang now exists as a cadastral community and locality within Gaishorn am See rather than as a separate administrative unit. Its administrative affairs are handled by the municipal authorities of Gaishorn am See.