Abstract: Border areas are important spaces for national security and opening up to the outside world, and the level of population security in these areas is related to border stability and regional sustainable development. Northeast China is a typical area of population shrinkage, and the problem of population shrinkage in border areas is even more prominent. Against the backdrop of population shrinkage, this paper takes 45 border counties (cities, districts) in Northeast China as an example, and uses the entropy method and multiple linear regression to assess the population security level in border areas and explore its influencing factors. The study found that: 1) From 2010 to 2020, the population of the north border area continuously declined and entered a stage of overall population shrinkage, with a total decrease of approximately 1.34 million over the decade. In particular, the border areas of Jilin Province experienced the widest and most severe population shrinkage. 2) The population security level in the north border area generally declined and exhibited significant spatial differentiation. Areas with relatively high population security were mainly concentrated in the northeast border areas of Heilongjiang Province, where openness and industrial development were relatively strong, whereas areas with low population security were concentrated in parts of the border areas of Jilin Province and Da Hinggan Ling Prefecture, where population loss was severe and the level of openness was relatively low. 3) Population security types can be classified into three categories: security stability, security improvement, and security decline, with the security decline type accounting for nearly one-third of the study area. 4) Population security is not solely determined by population size, but rather by the coordinated relationship among population quantity, structure, and regional development capacity. Economic development is the key factor affecting population security. Economic indicators such as nighttime light index and the proportion of secondary and tertiary industries have significant positive effects on population security, while natural and administrative factors also play certain roles. Finally, this study proposes differentiated governance strategies for different types of areas, with the aim of improving the population security level and maintaining border stability in the north border area.