According to the U.S. Census Bureau, the county has a total area of 4,017 square miles (10,400 km²), of which 3,987 square miles (10,330 km²) are land and 30 square miles (78 km²) (0.7%) are water.
It is the third-largest county in Colorado by area.

Weld County lies within the relatively flat eastern portion of Colorado; the northeastern portions of the county contain the extensive Pawnee National Grassland and the Pawnee Buttes, which jut  350 feet (110 m) above the surrounding terrain and are surrounded by many small canyons and outcroppings.
Along the western border, hilly areas indicate the presence of the foothills of the Rocky Mountains further west.

The county is served by two interstate highways: I-25 (US 87) runs through the southwestern corner and I-76 from the south central edge northeastward to the Morgan county border.
Other major roads include US 85 and US 34, which intersect near Greeley, and State Highway 14, which runs through Ault.
According to the U.S. Census Bureau, the county has a total area of 4,017 square miles (10,400 km²), of which 3,987 square miles (10,330 km²) are land and 30 square miles (78 km²) (0.7%) are water. It is the third-largest county in Colorado by area.
Weld County lies within the relatively flat eastern portion of Colorado; the northeastern portions of the county contain the extensive Pawnee National Grassland and the Pawnee Buttes, which jut  350 feet (110 m) above the surrounding terrain and are surrounded by many small canyons and outcroppings. Along the western border, hilly areas indicate the presence of the foothills of the Rocky Mountains further west.
The county is served by two interstate highways: I-25 (US 87) runs through the southwestern corner and I-76 from the south central edge northeastward to the Morgan county border. Other major roads include US 85 and US 34, which intersect near Greeley, and State Highway 14, which runs through Ault.
Weld County, Colorado