Originally, Millsap was established as a relay station on the stagecoach route that ran from Weatherford to Palo Pinto.

The town was named for Fuller Millsap, who moved to Texas in 1849 and to Parker County in 1856.

Millsap is located on Farm to Market Road 113, 15 miles west of Weatherford, in western Parker County.

According to the United States Census Bureau, the town has a total area of 1.3 square miles (3.4 km2), of which 99.24% is land and 0.76% is covered by water.

The climate in this area is characterized by relatively high temperatures and evenly distributed precipitation throughout the year.

The Köppen climate classification describes the weather as humid subtropical, Cfa.