Weld County is one of the 64 counties of the U.S. state of Colorado. As of the 2010 census, the population was 252,825. The county seat is Greeley.
According to the U.S. Census Bureau, the county has a total area of 4,017 square miles (10,400 km), of which 3,987 square miles (10,330 km) are land and 30 square miles (78 km) (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.
As of the census of 2000, there were 180,936 people, 63,247 households, and 45,221 families residing in the county. The population density was 45 people per square mile (18/km²). There were 66,194 housing units at an average density of 17 per square mile (6/km²). The racial makeup of the county was 81.71% White, 0.56% Black or African American, 0.87% Native American, 0.83% Asian, 0.08% Pacific Islander, 13.29% from other races, and 2.65% from two or more races. 27.05% of the population were Hispanic or Latino of any race.
There were 63,247 households out of which 37.20% had children under the age of 18 living with them, 57.60% were married couples living together, 9.40% had a female householder with no husband present, and 28.50% were non-families. 21.00% of all households were made up of individuals and 6.90% had someone living alone who was 65 years of age or older. The average household size was 2.78 and the average family size was 3.25.
In the county, the population was spread out with 28.20% under the age of 18, 13.20% from 18 to 24, 29.70% from 25 to 44, 20.00% from 45 to 64, and 9.00% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 100.60 males. For every 100 females age 18 and over, there were 98.00 males.
The median income for a household in the county was $42,321, and the median income for a family was $49,569. Males had a median income of $35,037 versus $25,757 for females. The per capita income for the county was $18,957. About 8.00% of families and 12.50% of the population were below the poverty line, including 14.60% of those under age 18 and 8.50% of those age 65 or over.