Cook School that was built in 1871 was the first school in the Commerce City area. In 1899 another school, Sand Creek School was added.

In 1907 Union High School was built by Adams City, Derby and Rose Hill school districts. Cook and Sand Creek Schools were sold and a new brick schoolhouse was built where the Adams City High School is now located. People felt that the four-room brick building was too elaborate for a country school and that there would never be enough young people to fill the school building.

Approximately a dozen pupils started classes in September of 1908. Ida Walker, the first teacher was paid a salary of $80 a month. Entertainment and graduation exercises for the new school were held at Platte Valley Hall that was located at 72nd Avenue and Dahlia Street. There were no school buses and students came to school in horsedrawn vehicles, carts, light spring wagons, horses, and by foot. There was a large shed for the animals. Some boys rode bicycles in good weather.

Arthur Hockmuth was one of two boys from Irondale in Union High School that first year, but because the Irondale District refused to support the school the parents were billed for tuition. When the tuition was not paid the two boys had to leave school.

Katherine M. Cook, State Superintendent of Schools helped pass an amendment in 1908 that required a school district that had no high school, to pay tuition in another district for students who wished to continue their education. Hockmuth, who wrote "The Genesis of a Country High School," said he was of the class of 1912 so he apparently was able to finish his schooling. Welby district maintained that the amendment was unconstitutional so those students who wanted to go to Union High School had to pay tuition of $2.50 a month.

Frances Pratt Douglass, the second teacher at Union High School began teaching in 1909 and taught there until 1918. Her salary was $100 a month. Mrs. Douglass, who came to Colorado because of her husband's poor health, was the only full time teacher in the school at that time. For the first four years there were fourteen students. The pupils in Mrs. Douglas' class wrote weekly news and sent the best items to the Brighton Blade for publication. Mrs. Douglas formed a girls club, put on plays and entertainments, and held reading and story-writing contests. She took the students on trips to various places of interest.

In 1910 the school had sixteen students. A Denver University student helped Mrs. Douglas four hours a week and was the basketball coach, Union High School's first sport. The students raised funds to buy a ball and baskets and small cottonwood trees, cut from the banks of the South Platte River, were used as basket supports. A boxcar door cut in half served as a backboard. No regular games were played the first year.

The next season students raised enough money to buy lumber and build better basket supports. Games were played at Brighton and Fort Lupton and four people who owned cars provided free transportation for the team and its cheering section. In the class of 1911 there were five seniors. The first part of a new high school building was built in 1916, with a large classroom, small office, storeroom and furnace room. There were 41 students then, and nine graduates.

In 1946 the surrounding districts consolidated to form School District No. 14 and Union High School became Adams City High School.