Knowlton was born March 5, 1912 and grew up on a dairy farm in San Antonio. At the age of 16, he started his own dairy farm at the corner of Braun and Leslie roads. He took college courses in dairy production and animal husbandry at Baylor and Purdue universities.
Knowlton Dairy soon became the largest independent producer of milk, ice cream, and butter in Texas. Knowlton married Roberta, a school teacher, and they had five children.
During World War II, Knowlton delivered milk on a Clydesdale horse to conserve gas. He was known as the milk man because he personally delivered milk to homes.
In the early 1950s, Knowlton convinced farmers and local business leaders of the need for the area's first high school, now Marshall High School. He served on the Northside Board of Trustees from 1949-1956.
Some of the community organizations he supported included Boy Scouts, Girl Scouts, March of Dimes, and United Way. He was a trustee and financial backer of Southwest Texas Methodist Hospital and served on the Board of Directors of the Methodist Home for Children. He was a charter member of Jefferson United Methodist Church and was known for inviting soldiers from Lackland AFB to his home so that they could eat a home-cooked meal. He also was active with the Bexar County Livestock Show and Rodeo.
Knowlton remained Chairman of the Board at Knowlton Dairy until 1979. In 1982, he received the Joe Freeman Award for Distinguished Service to the South Texas Agribusiness Industry, and in 1984, he was named to the Texas Dairy Producers Hall of Fame. He passed away in 1984, just before his namesake school opened.