Background: Addressing mental health illnesses among the college student population is pressing since they are associated with a decline in academic performance. Purpose: This cross-sectional study investigates the impact of mental health illnesses and test anxiety on academic performance of 201 undergraduate students post-COVID-19 in U.S.A. Methods: A survey was administered between October 20th and November 3rd 2022 to collect data on demographics, mental health variables and GPA. Results: Significant negative associations were observed between academic performance and depression ([beta] = -0.022, p < 0.01), anxiety ([beta] = -0.015, p = 0.01), stress ([beta] = -0.021, p < 0.01), and test anxiety ([beta] = -0.011, p < 0.01). There was a significant difference in GPA between all labels of depression and stress (P = 0.01 and P < 0.01 respectively). For test anxiety and GPA, there was significant dose response relationship; the higher the test anxiety level, the lower the GPA (P < 0.01). Discussion: Governments and higher education institutions should provide the necessary academic, social, mental, and financial support during and post-confinement. Translation to Health Education Practice: The findings may be valuable for health educators who can reach stakeholders and highlight the importance of addressing these mental health illnesses and applying systematic mental health treatment plan on college campuses.