Welby is a census-designated place (CDP) in Adams County, Colorado, United States. The population was 14,846 at the 2010 census.
The community was named after one General Welby, a railroad official.
According to the United States Census Bureau, the CDP has a total area of 3.8 square miles (9.8 km2), of which 3.7 square miles (9.6 km2) is land and 0.12 square miles (0.3 km2), or 2.74%, is water.
As of the census of 2000, there were 12,973 people, 4,614 households, and 3,248 families residing in the CDP. The population density was 3,379.5 people per square mile (1,304.4/km2). There were 4,771 housing units at an average density of 1,242.9 per square mile (479.7/km2). The racial makeup of the CDP was 71.46% White, 1.58% African American, 1.76% Native American, 1.18% Asian, 0.12% Pacific Islander, 19.32% from other races, and 4.58% from two or more races. Hispanic or Latino of any race were 36.94% of the population.
There were 4,614 households, out of which 36.5% had children under the age of 18 living with them, 49.1% were married couples living together, 15.0% had a female householder with no husband present, and 29.6% were non-families. 22.3% of all households were made up of individuals, and 4.9% had someone living alone who was 65 years of age or older. The average household size was 2.80 and the average family size was 3.28.
In the CDP, the population was spread out, with 28.3% under the age of 18, 11.2% from 18 to 24, 33.4% from 25 to 44, 19.1% from 45 to 64, and 8.0% who were 65 years of age or older. The median age was 30 years.