The development and the calibration of a microscopic traffic simulation model, using MITSIMLab, for the entire metropolitan area of Des Moines, Iowa, are presented. The primary contributions include the application of a microscopic model on such a large-scale network and an effort for joint calibration of the model parameters and estimation of origin-destination flows. The application of microscopic traffic simulation models to very large networks such as this poses a number of methodological and practical challenges that are not faced with smaller applications. Solutions to these problems are both heuristic and analytical. The solutions presented are generic and hence applicable to any large-scale microscopic traffic modeling.