Methods to estimate abundance and density of Columbian black-tailed deer (Odocoileus hemionus columbianus) are limited. Regional wildlife managers are concerned that Columbian black-tailed deer on Whidbey Island, Washington, USA, exceed carrying capacity. Research on small islands in the Pacific Northwest reports high deer densities; however, these islands are smaller and less complex than Whidbey Island, and have fewer mortality sources. Our objective was to estimate the abundance and density of Columbian black-tailed deer on Whidbey Island by using road-based spotlight surveys in a distance sampling framework. We conducted spotlight surveys from 12 January 2015 to 23 January 2015 starting ≤1 h after sunset and continuing to 23:00. The deer population of Whidbey Island is estimated to be 2744.5 individuals (6.2 deer/km²), lower than estimated densities of deer on smaller islands in the region. Density varied across the different sections of Whidbey Island. Road-based spotlight surveys in a distance sampling framework are a useful tool for estimating deer populations in regions where traditional monitoring methods are not practical. This research offers baseline estimates for the deer on Whidbey Island and provides a repeatable procedure to estimate abundance and density.