The Somerset Choices website, run by Somerset County Council, will see approved and vetted carers list the types of services they can offer.
The National Care Association said if listed carers fell ill or took holiday, there could be gaps in service.
Somerset County Council said steps were in place to mitigate against this.
The two-year project - which lists services on a website - has been prompted by the introduction of the Care Act 2014, which came into force in April.
By law, councils must develop new markets which can offer a range of choices for those needing care.
Nadra Ahmed, chair of the National Care Association, said: "There is a concern over the continuity of service.
"If these are single employers with 'single' roles, if something happens to them, are we going to find people left at critical periods of time without any support?"
She said there were also issues with how well-trained the self-employed carers were.
Gareth O'Rourke, senior manager at the council, said: "[The service] is for a group of people who have a very good understanding of their needs and a strong understanding of how they want their needs to be met."
He added those on the register were vetted, insured and met self-employment law criteria.
According to Somerset County Council, the number of people likely to need support will rise from 2,392 in 2011, to 2,751 in 2015.
In 2011/12, about 58,300 people provided unpaid care.
It is not known how many people need care in the county as some pay for it privately and have no contact with social services.
Somerset Choices offers services from personal care to dog walking.
A council project to boost the number of "sole trader" carers for the elderly may leave people without support, a care association has said.