Over the past few decades, strong debates regarding the interpretations of implicit associations (e.g., personal beliefs versus cultural associations) and their ability to be malleable but not permanently changed have taken place. Past research long established the importance of immediate situational influences (e.g., background of environment, target prototypicality) on various implicit biases, such as the Black-weapon stereotype. However, to date, relatively few studies have investigated the influence of contextual effects (e.g., ethnic diversity, violence rates) on implicit biases. Building on evidence from cross-sectional research, the current study aimed to investigate the longitudinal relationship between context diversity and implicit Black-weapon associations by undertaking a more sophisticated analytical approach accounting for both individual and contextual variations in implicit Black-weapon associations over time. Multilevel models on the repeated cross-sectional design demonstrated that implicit Black-weapon associations have decreased over the course of a decade, specifically from 2009 to 2018, and to a greater extent in areas that had greater increases in variety over time. Supplementary analyses were run to test the moderating effect of participant ethnicity, in which the results indicated that participant ethnicity explained some variation in implicit Black-weapon associations, albeit the effect sizes were below the threshold and did not affect the main findings. The present study replicated cross-sectional patterns from past research while simultaneously providing evidence of a decreasing trend in implicit Black-weapon associations over the 10-year period. We discuss how the findings align with prior research examining the relationship between ethnic diversity and bias, as well as add to the nascent literature on the socio-structural foundations of implicit biases.