Importance: The COVID-19 pandemic led to sharp declines in cancer screening. However, the total deficit in screening in the US associated with the pandemic and the differential impact on individuals in different geographic regions and by socioeconomic status (SES) index have yet to be fully characterized. Objectives: To quantify the screening rates for breast, colorectal, and prostate cancers associated with the COVID-19 pandemic in different geographic regions and for individuals in different SES index quartiles and estimate the overall cancer screening deficit in 2020 across the US population. Design, Setting, and Participants: This retrospective cohort study uses the HealthCore Integrated Research Database, which comprises single-payer administrative claims data and enrollment information covering approximately 60 million people in Medicare Advantage and commercial health plans from across geographically diverse regions of the US. Participants were individuals in the database in January through July of 2018, 2019, and 2020 without diagnosis of the cancer of interest prior to the analytic index month. Exposures: Analytic index month and year. Main Outcomes and Measures: Receipt of breast, colorectal, or prostate cancer screening. Results: Screening for all 3 cancers declined sharply in March through May of 2020 compared with 2019, with the sharpest decline in April (breast, -90.8%; colorectal, -79.3%; prostate, -63.4%) and near complete recovery of monthly screening rates by July for breast and prostate cancers. The absolute deficit across the US population in screening associated with the COVID-19 pandemic was estimated to be 3.9 million (breast), 3.8 million (colorectal), and 1.6 million (prostate). Geographic differences were observed: the Northeast experienced the sharpest declines in screening, while the West had a slower recovery compared with the Midwest and South. For example, percentage change in breast cancer screening rate (2020 vs 2019) for the month of April ranged from -87.3% (95% CI, -87.9% to -86.7%) in the West to -94.5% (95% CI, -94.9% to -94.1%) in the Northeast (decline). For the month of July, it ranged from -0.3% (95% CI, -2.1% to 1.5%) in the Midwest to -10.6% (-12.6% to -8.4%) in the West (recovery). By SES, the largest screening decline was observed in individuals in the highest SES index quartile, leading to a narrowing in the disparity in cancer screening by SES in 2020. For example, prostate cancer screening rates per 100 000 enrollees for individuals in the lowest and highest SES index quartiles, respectively, were 3525 (95% CI, 3444 to 3607) and 4329 (95% CI, 4271 to 4386) in April 2019 compared with 1535 (95% CI, 1480 to 1589) and 1338 (95% CI, 1306 to 1370) in April 2020. Multivariable analysis showed that telehealth use was associated with higher cancer screening. Conclusions and Relevance: Public health efforts are needed to address the large cancer screening deficit associated with the COVID-19 pandemic, including increased use of screening modalities that do not require a procedure.