- In 1960 the first library opens in Thornton.
- In 1960 the population is 11,353.
- In 1961, the City moved forward with issues including the running of day-to-day City operations by adopting a City Manager form of government, and securing a City water supply.
- In 1962, the Thornton Junior Football League was formed.
- In April 1963, Thornton purchases the Northwest Utilities.
- In July 1963, the City held the first Thornton Annual Festival Days celebration and an estimated 8,000 people attended.
- In 1964, the City annexed approximately 920 acres on both sides of the Valley Highway
(I-25) including the Heftler Hillcrest area and land between 88th and 92nd Avenues.
- In 1964 Thornton considers a name change, but the idea fizzles.
- In 1965, Thornton selected a city seal by holding a City Seal Contest that was open to all Thornton public school children. The winner was a 17-year-old Mapleton High School student. That May, the winning seal with the motto "City of Planned Progress" was adopted.
- In 1966, a home-rule committee was formed.
- On July 18, 1967, Thornton citizens overwhelmingly approved Home Rule for the City. A Home Rule city has its charter (constitution) written by local citizens and the voters must approve it. Home Rule gives local government more control over running the city.
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