Tufts Health Plan is teaming up with a Hartford-based health care system to launch a company to sell health insurance in Connecticut.

Tufts and Hartford HealthCare said their venture, which they’re calling CarePartners of Connecticut, will target a growing market of adults 65 and older.

Tufts, one of Massachusetts’ largest health insurers, and Hartford HealthCare, one of Connecticut’s largest medical networks, will split the costs and the revenues of their nonprofit company.

The arrangement allows both organizations to share the risks of entering a new market. Tufts chief executive Thomas A. Croswell said that instead of going it alone, the insurer wanted to partner with a health care provider that was well-known in Connecticut and committed to working on coordinating patient care and containing costs.

“There is tremendous concern on the cost of health care and the cost of health insurance, so you’re seeing an increasing pressure on health plans and providers to find ways to address that,’’ Croswell said.

“We believe firmly there is an opportunity by working together more effectively.’’

Executives at Hartford HealthCare said they hope to attract members to the new insurance company by offering a one-stop shop: a single phone number to call for answers about both insurance costs and medical care.

Hartford HealthCare will continue to accept patients with other Medicare coverage plans.

“This, we think, is going to be a powerful opportunity to manage their care journey,’’ said Elliot Joseph, chief executive of Hartford HealthCare.

The new venture will compete in Connecticut with several large national insurers and will begin selling coverage in October, pending approvals.

Tufts Health Plan launched a similar venture in New Hampshire in 2015.

In Massachusetts and elsewhere in the country, some health care providers have partnerships with insurance companies — even running their own insurance businesses, in some cases.

The lines between insurers, providers, and other health care companies continue to blur, with CVS Health saying in December that it planned to buy the insurance giant Aetna. That deal is awaiting federal approval.

Priyanka Dayal McCluskey can be reached at priyanka.mccluskey@globe.com. Follow her on Twitter @priyanka_dayal.