A good structural knowledge of heritage buildings is a key factor for their conservation and for the planning of retrofit interventions, especially in high seismic risk areas, like Italy. Within this context, structural health monitoring techniques, like those based on ambient vibrations under operating conditions, represent a powerful tool for evaluating the dynamic behavior of existing structures. This methodology is particularly interesting for historic and monumental buildings due to its non-invasiveness. Starting from experimental vibration measurements, modal properties of the investigated building (natural frequencies, damping ratios and mode shapes) can be identified through operational modal analysis. Moreover, the results of output-only identification tests can be used for the setting and validation of refined finite element numerical models, through the tuning of some selected parameters. The availability of a reliable numerical model, able to represent the behavior of the building in its current state, together with dynamic surveys repeated over time, can be also useful for civil protection purposes, allowing to detecting and interpreting possible failures and damages. Within this context, this work illustrates the installation of a monitoring system in the historical masonry Town-Hall of Borgo Val di Taro, dating back to the fifteen century, for its ambient vibration modal identification. The so collected data are then used for the construction and updating of a refined numerical model for the simulation of the dynamic response of the building.