College students today suffer more than ever from depressive symptoms. This web‐based survey collected both subjective self‐reported and objectively measured mobile screen time from smartphones' screen time reporting feature from 426 and 175 college students, respectively. Depressive symptoms were measured by the 10‐item Center for Epidemiologic Studies Short Depression Scale. Logistic regression models were used to estimate odds ratios (OR) and 95% confidence intervals (95% CI), adjusting for gender, race/ethnicity, age, employment, first‐generation student status, sexual orientation, social support, and social ladder. Compared to those with 3.05 or fewer hours of objectively measured daily mobile screen time, those with 3.10–5.68 hr did not have increased odds of depressive symptoms, while those with more than 5.72 hr had significantly higher odds, (OR: 3.49, 95% CI: 1.24–9.86). Restricted cubic spline of the association between objectively measured daily mobile screen time and depressive symptoms further confirms the threshold effect—the probability of depressive symptoms holds relatively steady until about 5 hr of daily mobile screen time and then shows a sharp rise. Findings suggest a nonlinear relationship between mobile screen time and depressive symptoms which, despite a moderate positive correlation between self‐reported and objectively measured average daily mobile screen time (r = .51, p < .001), has not be captured using self‐reported mobile screen time. Future studies should objectively measure mobile screen time and college students at risk for depressive symptoms should consider limiting their mobile screen time to about 5 hr per day.