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.

Ms Davies appeared as Mrs Perks in the Railway Children and as Marj in the valleys-based comedy Stella.
Tony Gardner, who appeared in Stella, wrote on Twitter: "Terribly saddened to hear Deddie Davies has died. She was a truly wonderful person."
Karen Paullada, who also appeared in the Sky 1 series, wrote: "Sad times in this happy Christmas period."
Stella star and co-creator Ruth Jones paid tribute to her "remarkable" co-star.
She said: "Deddie had been ill for a long time and I saw her about a month ago and showed her the Christmas special on my laptop.
"She loved working on Stella. She said it kept her going and she was massively loved by all the cast and crew.
"She was one of those rare people who didn't possess a grain of self pity and whose company always brightened your day.
"A highly intelligent, joyful, talented and spectacularly spirited woman, who was an inspiration to us all."
She added Ms Davies would be "unspeakably missed".
Ms Davies had been a well-known face on TV screens since the 1970s, appearing in shows including The Forsyte Saga, The Bill, Upstairs, Downstairs, Grange Hill and Whitechapel.
Her agents, Brown, Simcocks and Andrews, said the actress also dedicated her time working with charities safeguarding the elderly and also "going undercover" to reveal issues in care homes.
Kelly Andrews, part of the team who represented Ms Davies for about 20 years, said: "She was extremely professional, but she was extraordinary fun and joyous to be around.
"She saw the best in everyone. She wasn't just an actress but an activist - she really cared about it."
A council project to boost the number of "sole trader" carers for the elderly may leave people without support, a care association has said.
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Tributes have been paid to Bridgend-born actress Deddie Davies, who has died at the age of 78.