MobileCity is a lightweight simulation platform designed to model realistic urban mobility. It introduces a comprehensive transportation system encompassing multiple modes of transportation and constructs agent profiles using survey data. To ensure scalable simulations, agents make action choices within a pre-generated action space and utilize local models for efficient agent memory generation. Extensive evaluations with 4,000 agents demonstrate that MobileCity generates more realistic urban behavior than existing models while maintaining computational efficiency. Practical applications, such as predicting travel patterns and analyzing demographic trends in transportation preferences, are explored.