Smithfield is a borough in Fayette County, Pennsylvania, United States. The population was 875 at the 2010 census. It is served by the Albert Gallatin Area School District. The town's largest employer is a small wire producing plant run by Nelson Steel.
Smithfield is located in southwestern Fayette County at 39°47′59″N 79°48′30″W (39.799664, -79.808197). According to the United States Census Bureau, the borough has a total area of 0.71 square miles (1.84 km2), all of it land.
U.S. Route 119 passes through the center of the borough, leading northeast 9 miles (14 km) to Uniontown, the county seat, and southwest 8 miles (13 km) to Point Marion.
As of the census of 2000, there were 854 people, 363 households, and 234 families residing in the borough. The population density was 1,196.5 people per square mile (464.4/km²). There were 384 housing units at an average density of 538.0 per square mile (208.8/km²). The racial makeup of the borough was 99.65% White, 0.23% African American and 0.12% Pacific Islander.