Fine particulate matter (PM2.5) posed adverse effects on human health and caused visibility degradation. Studies have indicated that impact of PM2.5 on human health and visibility showed spatial heterogeneity. Moreover, the contributions of different PM2.5 chemical compositions to its environmental effects varied on regional scale. Therefore, it is important to understand the spatiotemporal variations of PM2.5 and its chemical compositions to assess the regional impacts of PM2.5. Secondary inorganic PM2.5 (iPM2.5) is formed through chemical reactions between base gas NH3 and acidic gas pollutants (e.g., NO2, SO2). The major compositions of iPM2.5 included NH4+, SO42-, and NO3-. To fully understand the regional impacts of PM2.5, this research was to quantify the spatiotemporal variations of iPM2.5 aiming to provide important evidence regarding contributions of iPM2.5 to PM2.5 in North Carolina (NC) Region. Measured PM2.5 concentrations at 34 sites and its chemical components at 7 sites in NC in 2005-2014 were extracted from EPA’s AirData. The data analysis indicated that higher PM2.5 concentrations occurred in central NC urban areas. Significant PM2.5 concentrations reduction occurred over the past 10 years. The temporal reduction trend of iPM2.5 was consistent with PM2.5 concentrations. Seasonal variation analysis indicated that PM2.5 concentrations were higher in summer and lower in winter; however, this seasonal variation was only significant in 2005-2011. The analysis of the relative contributions of PM2.5 chemical compositions to the total PM2.5 mass showed that iPM2.5 was the dominant part of PM2.5 in 2005-2011; however, organic carbon matter (OCM) dominated in 2012-2014. Furthermore, significant seasonal variations of iPM2.5 mass fraction were observed, NO3- and SO42- exhibited inverse seasonal variation. This study reveals the spatiotemporal variations of PM2.5 and its associated chemical compositions in NC, which provides insights to link the ambient PM2.5 to various sources for development of control and mitigation strategies.