By relating the ground state of Temperley-Lieb hamiltonians to partition functions of 2D statistical mechanics systems on a half plane, and using a boundary Coulomb gas formalism, we obtain in closed form the valence bond entanglement entropy as well as the valence bond probability distribution in these ground states. We find in particular that for the XXX spin chain, the number Nc of valence bonds connecting a subsystem of size L to the outside goes, in the thermodynamic limit, as Nc (Ω) = 4 π 2 ln L, disproving a recent conjecture that this should be related with the von Neumann entropy, and thus equal to 1 3 ln 2 ln L. Our results generalize to the Q-state Potts model. Introduction. Entanglement is a central concept in quantum information processing, as well as in the study of quantum phase transitions. One of the widely used entanglement measures is the von Neumann entanglement entropy S vN , which quantifies entanglement of a pure quantum state in a bipartite system. To define S vN precisely, let ρ = |Ψ Ψ| be the density matrix of the system, where |Ψ is a pure quantum state. Given a complete set X of commuting observables, let X = A ∪ B be a bipartition thereof. Then S vN is defined as