The security concerns surrounding the 2016 and 2020 United States Presidential Elections have underscored the critical importance of election security, prompting a renewed emphasis on preventing, detecting, and mitigating emerging threats associated with election infrastructure. With their pivotal role as the first line of defense on Election Day, poll workers bear the responsibility of identifying and thwarting any potential threats that may arise. Moreover, they possess unsupervised access to the U.S. critical infrastructure elections equipment at polling places and are entrusted with administering the election processes at their local precincts. However, despite their crucial role, poll workers receive minimal, if any, specific training on security threats prior to elections. To address this gap, this research investigates poll worker threat awareness through developing, piloting, and empirically evaluating online training modules aimed at teaching poll workers to identify and mitigate potential cyber, physical, and insider threats that may arise prior to, and on, Election Day. Through statistical analysis of a pre-post-test study involving eligible and current poll workers, this research demonstrates the effectiveness of these training modules to significantly enhance poll workers' understanding of cyber, physical, and insider threats associated with the processes of three critical areas in voting: electronic pollbooks, the scanning unit, and provisional voting. The implications of this work emphasize the need for resources for election officials and managers to provide effective and comprehensive poll worker training and, thus, ensure the security and integrity of U.S. election processes.