The recent introduction of the Asian giant hornet (Vespa mandarinia Smith) in the United States in late 2019 has raised concerns about its establishment in the Pacific Northwest and its potential deleterious effects on honey bees and their pollination services in the region. Therefore, we conducted a risk assessment of the establishment of V. mandarinia in Washington and Oregon on a county-by-county basis. Our tier-1 qualitative and semi-quantitative risk assessment relied on the biological requirements and ecological relationships of V. mandarinia in the environments of the Pacific Northwest. We based the risk characterization on climate and habitat suitability estimates for V. mandarinia queens to overwinter and colonize nests, density and distribution of apiaries, and locations of major human-mediated introduction pathways that may increase establishment of the hornet in the counties of Washington and Oregon. Our results suggest that 5 counties in the region could be at low risk, 48 at medium risk, and 22 at high risk of establishment. For Washington, counties at high risk included Clallam, Clark, Cowlitz, Grays Harbor, King, Pierce, Skagit, Snohomish, and Whatcom. The high risk Oregon counties included Benton, Clackamas, Clatsop, Coos, Douglas, Hood River, Lane, Lincoln, Linn, Marion, Multnomah, Polk, and Yamhill. Many of the western counties of both Washington and Oregon were estimated to be at the highest risk of establishment mainly due to their suitable climate for queens to overwinter, dense forest biomass for nest colonization, and proximity to major port and freight hubs in the region. Considering its negative effects, these counties should be prioritized in ongoing monitoring and eradication efforts of V. mandarinia.