Does democracy increase the level of public health? The positive influence of democracy on the level of public health has been widely studied. Yet, related to developing countries, only few research empirically examined this relationship. With the subnational data on the number of under-5 mortalities per 1,000 live births in Nigeria from 2000 to 2020, this article using ordinary least squares (OLS) regression models demonstrates that subnational democracy leads to a higher subnational level of public health. In addition, we find that, if a president and a state governor have the same party affiliation, inter-government cooperation is facilitated and, in turn, it is translated into a higher subnational level of public health. More interestingly, this relationship is strengthened by the subnational democracy.