The national population census plays a crucial role in providing a comprehensive understanding of a country's development and aids in policymaking and planning. However, any shortcomings in the census system can have adverse effects on the country. Our previous research has highlighted several flaws in the current census systems, such as inadequate population coverage, racial and ethnic biases, data privacy and security issues, and problems with data distribution. These issues can be mitigated through the implementation of Blockchain technology. By using a Blockchain-based system for conducting the national population census, transparency, privacy, and authenticity can be ensured while maintaining data integrity, security, efficiency, and trustworthiness. This paper builds upon our ongoing research that identifies the primary challenges the current centralized census systems face through a systematic literature review and structured interviews conducted with Pakistan's national census bureau. In this paper, we present a Blockchain-based system architecture that addresses the identified challenges and meets the requirements of Pakistan's national census bureau.