The U.S. Geological Survey (USGS) is developing SPARROW models (SPAtially Related Regressions On Watershed Attributes) to assess the transport of contaminants (e.g., nutrients) through the Pacific drainages of the United States (the Columbia River basin; the coastal drainages of Washington, Oregon, and California; the Klamath River basin; the Central Valley of California, and the west slopes of the Sierra Nevada Mountains). SPARROW relates instream water quality measurements to spatially referenced characteristics of watersheds, including contaminant sources and the factors influencing terrestrial and aquatic transport. The population of livestock within a watershed is a potential factor affecting nutrient delivery to streams. The spatial data set “County-level livestock data for the Pacific drainages of the United States (2012)" summarizes livestock populations and the associated generation of manure nutrients for each county lying partially or fully within Pacific drainages of the United States. This data set was created by combining an existing data set of county-level livestock and manure nutrient data for the United States with regional information on cattle housed in dairies and feedlots.