Data presented are results of surveys (2015 and 2016) and monitoring (2016) for Southwestern Willow Flycatcher (Empidonax traillii extimus) in San Diego County, California. In 2015, surveys were conducted at select locations along the San Luis Rey River between College Boulevard and Lake Henshaw. In 2016, surveys were conducted at select locations along Agua Hedionda Creek, San Dieguito River, San Luis Rey River, Santa Ysabel Creek, and San Diego River, and nest monitoring was performed at three locations along the San Luis Rey River downstream of Lake Henshaw (Cleveland National Forest, Rey River Ranch, Vista Irrigation District). Surveys were conducted along multiple sections of the river where permission to access properties could be obtained. Locations were surveyed using a standardized protocol three to four times between 15 May and 31 July. The number, age (adult or juvenile), sex, banding status (color banded or not, and if so, color combination), and breeding status (paired, undetermined, or transient) of all willow flycatchers was recorded. In 2015, as preparation for nest monitoring in 2016, adult flycatchers (when possible) were captured in mist nets, using song playbacks to attract birds to nets, and color banded with individually unique color combinations to provide data on survival within and between years. Nestlings in nests found opportunistically during surveys were banded at 6-8 days of age. During banding, data were collected on age, sex, weight, and reproductive status. The goal of nest monitoring was to collect data on annual productivity. Monitored territories were visited 1-2 times weekly to determine nest success and band the nestlings at 6-8 days of age. Adults were also color banded as described above to examine survivorship and dispersal patterns.