The search for a reliable data-set of entrepreneurial firms is ongoing. We analyze and assess longitudinal data on startups from two data sources – the National Establishment Time-Series (NETS) database and the Secretary of State (SOS) business registry data. Our primary purposes in this paper are to assess the usefulness and reliability of these databases in measuring startup activity along several quality indicators and to explore the possibility of integrating these large databases using both automated and manual processes. The NETS identifies a firm’s employment, sales, and industry but is expensive and suffers from a temporal lag. The SOS data provide up-to-date startup counts but offer limited variables. We conclude that policymakers and researchers will benefit from combing both the SOS and adjusted NETS since they provide complementary information on startups. We carefully document our methodology and make suggestions for use of the data for future research.