The school, together with county runners-up Shenfield High School, will represent Essex in the regional final to be held at Hassenbrook School in Stanford le Hope on January 30.
The Chelmsford team, made up of captain Megan Clark, Abigail Ashford, Nicole Leonhardt, Flora Raybould, Eleanor Jones, Ellie Crawley, Lucy Spence, Alex Buckley, Charlotte Everett and Clara Tanner, won the Essex final by beating Shenfield 8-7.
Sarah Bellamy, head of PE at Chelmsford County High School, said: "We are extremely proud of our girls in the under-14 squad, they worked tremendously hard on the day and through excellent teamwork they triumphed.
"We are thoroughly looking forward to the regional round where we will be proudly representing Essex."