Thornton consisted solely of farmland until 1953 when Sam Hoffman purchased a lot off Washington Street about seven miles north of Denver.
Thornton was named in honour of then-incumbent Colorado Governor Dan Thornton.
The Thornton Community Association was formed in 1954 to help guide the new community’s development. By 1955, Thornton had 5,500 residents in over 1,200 homes.
Thornton was incorporated in 1956 as a city. Oyer G. Leary was elected the first mayor.
Thornton is located at 39°54′11″N 104°57′16″W (39.903043, -104.954406).
Thornton has a total area of 24,286 acres including 1,295 acres of water.
The estimated population of Thorton is 141,867, as of 2020, making Thornton the sixth most populous city in Colorado and the 191st most populous city in the United States.
Thornton has 81 city parks and nearly 2,000 acres of parks and open space.
Thornton is served primarily by three school districts: Adams County School District 12, Mapleton Public Schools, and Brighton School District 27J.
Notable individuals born in or have lived in Thornton include Tesho Akindele, Josh Bredl, Edward Casso, John Denney, Beth Martinez Humenik, Mike Manning, Nikki Marshall, Mike McCoy, Adrian Mora, Joseph Salazar, Kyle Sleeth, Neal Ulevich.