Wellersburg is located at the extreme southern end of Southampton Township, along its border with Maryland.

Pennsylvania Route 160 passes through Wellersburg as it runs between the Maryland border to the south and Southampton Township to the north.

According to the United States Census Bureau, the borough has a total area of 0.8 square miles (2.1 km2), all land.

At the time of the 2000 census, there were 176 people residing in eighty-four households in the borough, including fifty-one families.

Approximately 4.3% of families and 5.4% of the population were living below the poverty line, including those who were aged sixty-five or older.