Just a quarter of education, health and care plans for disabled children and young people in Cornwall were prepared within the legal time limit last year, new figures show.
The plans allow families to access tailored assistance for children and young people with disabilities and special educational needs. Disability charity Sense said delays in creating these plans means thousands of youngsters are at risk of "falling through the cracks".
By law, councils have 20 weeks from the date of a request being made to craft a plan.
However, Department for Education data shows 26% of education, health and care plans in Cornwall last year were created within 20 weeks.
It was down significantly from 91% of care plans in 2021.
Sarah White, Sense head of policy, said: "EHC plans are vital for disabled children to access support which enables them to thrive. Without them, education, health and care services are limited in what support they can provide and children won’t get the best start in life."
"It is hugely disappointing that nearly half of families are not receiving this plan within the legal time limit," she added.
"This leaves thousands of disabled children at risk of falling through the cracks, with potentially catastrophic knock-on effects on their education and health, which could have lifelong consequences."
Across England, the rate of plans issued within the 20-week limit fell to 51% last year, down from 60% in 2021 and the lowest level since 2015.
Louise Gittins, chair of the Local Government Association’s Children and Young People Board, said the figures are a reminder of the strain the special educational needs and disability system is under.
She added the Government responded to calls to set out an improvement plan this year for the system, but said it does not go far enough to address cost and demand issues councils are struggling with.
"Improving levels of mainstream inclusion will be crucial to the success of any reforms, reducing the reliance on costly special schools and other settings," she added.
A Department for Education spokesperson said the improvement plan committed to a wide range of actions to make sure education, health and care plans are available in a timely way for those who need them.
"We are now working hard to quickly deliver this reform, tackling the issues within the system exacerbated through the pandemic, to make sure that children get the extra support they need earlier and more consistently across the country," they said.