Achyranthes japonica (Miq.) Nakai (Japanese chaff flower) is a relatively new, invasive species to the United States, with limited information on its life history characteristics. The purpose of this study was to assess the importance of seed survivorship in the soil of A. japonica and to compare survivorship, fecundity, and morphological characteristics within populations at two different sites, Chestnut Hills Nature Preserve (CH) and Bellrose Waterfowl Reserve (BWR), in southern Illinois. Plots were established at each site to determine seed viability by burying seed bags over each of three winters (2012 to 2014) to quantify seedling emergence in the latter 2 yr (2013 and 2014) and to monitor survival of three cohorts of 50 seedlings per site starting in 2012, 2013, and 2014. In addition, 20 reproductive adults were selected outside of the plots to determine average fecundity and to measure a suite of morphological characteristics. Environmental factors had a significant effect on seed viability, which decreased from 2012 to 2013 during a drought year and rebounded from 2013 to 2014 following flooding. On average, individuals at the CH site had higher performance and fecundity when compared with individuals at BWR, regardless of year. Additional differences among the sites, such as dryness, disturbance, and species composition, most likely affected plant performance (i.e. plant height, number of nodes and stems, and inflorescence length). Regardless of high between-population variability, this invasive species has high fecundity, high seed viability, and high propagule pressure that allow rapid spread and expansion of its invasive range. More research is needed on the soil seedbank, seed dormancy, and the effects of stress, which will allow more-informed methods of control.