We consider functions of multi-dimensional versions of truncated Wiener-Hopf operators with smooth symbols, and study the scaling asymptotics of their traces. The obtained results extend the asymptotic formulas obtained by H. Widom in the 1980's to non-smooth functions, and non-smooth truncation domains.The obtained asymptotic formulas are used to analyse the scaling limit of the spatially bipartite entanglement entropy of thermal equilibrium states of non-interacting fermions at positive temperature.2010 Mathematics Subject Classification. Primary 47G30, 35S05; Secondary 45M05, 47B10, 47B35. Key words and phrases. Non-smooth functions of Wiener-Hopf operators, asymptotic trace formulas, entanglement entropy.The non-smooth generalizations are partly motivated by new applications of the Szegő asymptotics in Statistical Physics, connected with the entanglement entropy for free fermions (EE), see [2], [3], [5], [6] and references therein. In particular, the asymptotic trace formula for smooth symbols a (i.e. the one in Theorem 2.3) is used to describe the EE at a positive temperature (see [6]) , whereas the zero temperature case requires the use of discontinuous symbols (see [5]). We briefly comment on these applications after the main Theorem 2.3.The paper is organized as follows. In Sect. 2 we provide some preliminary information and state the main result, followed by a short discussion of the applications to the EE. It is not so trivial to see that the main asymptotic coefficient B d (a, ∂Λ; f ) is finite, if the function f is non-smooth. This point and other useful properties of B d (a, ∂Λ; f ) are clarified in Sect. 3. In Sect. 4 we collect some known and some new bounds for trace norms of Wiener-Hopf operators. Among other bounds, Sect. 4 contains the crucial trace-norm estimate for the operator (1.