Irregular migration is the migration of people across national borders in a way that violates the immigration laws of the destination country. Recently, it has been noted that there is a rising trend in irregular migration worldwide, especially from poorer to richer countries. Most migrants within and outside Africa are irregular migrants. However, those found in Nigeria appear to be on the increase in recent time, especially in the North-Western region. The purpose of this paper is to examine the issue of irregular migration and its effects on Nigeria's national security with particular reference to the North West region, and with a view of providing suggestions on how the security challenges faced in the country could be addressed. Thus, the paper began by presenting a historical and conceptual background of the issue of irregular migration and security challenges in Nigeria. The trends and issues of irregular migration and security challenges in North-Western Nigeria were reasonably discussed. It then reviewed the causes of irregular migration. It specifically dwelt extensively on the impacts and consequences of irregular migration on social, economic, political, and security.