Newsroom · South Dakota

Aetna Medicare Advantage Leaving 24 South Dakota Counties in 2027

Aetna is pulling its Medicare Advantage plans back to the southeast corner of the state for 2027. If you're in an Aetna plan around Mitchell, Huron or anywhere outside that corner, this is about your plan.

Big Sioux Benefits Data Desk

Published September 29, 2026 · 10 min read · Sourced from CMS.gov and Medicare.gov

Aetna Medicare Advantage is leaving 24 South Dakota counties for 2027 and staying in 10, all in the southeast. If you're in an Aetna Medicare plan in a county like Davison, Beadle, Spink or Charles Mix, your plan won't be offered there on January 1, 2027. You still have Medicare. You still have choices in your county. What you don't have is the option of doing nothing and keeping what you have.

We built this page from two CMS files: the CY2026 Medicare Advantage landscape and the CY2027 landscape, both the September 2026 release, filtered to South Dakota and compared county by county. The enrollment rules come straight from Medicare.gov and CMS publications. Nothing here is estimated.

A few terms, defined once

• Medicare Advantage (Part C). A private plan that replaces Original Medicare for your hospital and doctor coverage, usually with drug coverage built in. Aetna's plans here are PPOs.
• Service area. The counties where a plan is sold. A plan can keep running and still drop your county, which is what is happening here.
• Annual Notice of Change (ANOC). The letter every continuing plan mails by September 30 showing next year's changes. We walk through one line by line in our 2027 ANOC guide.
• D-SNP. A Dual Eligible Special Needs Plan, only for people who have both Medicare and Medicaid.
• Medicare Cost plan. A different kind of private Medicare plan that still lets you use Original Medicare outside its network. Several of the plans left in these counties are Cost plans.
• Landscape file. CMS's public spreadsheet of every Medicare Advantage plan in every county for a plan year. It is the source for every count on this page.

Where Aetna stays and where it leaves

For 2027, Aetna offers Medicare Advantage plans in 10 South Dakota counties: Brookings, Clay, Lake, Lincoln, McCook, Minnehaha, Moody, Turner, Union, Yankton. That is Sioux Falls and the counties around it, down to Vermillion and Yankton and up to Brookings. In 2026 the same five Aetna plans reached 34 counties, stretching north to Marshall and Walworth and west to Corson and Gregory.

The 24 counties Aetna leaves are: Aurora, Beadle, Bon Homme, Brule, Buffalo, Campbell, Charles Mix, Clark, Corson, Davison, Day, Deuel, Douglas, Gregory, Hamlin, Hanson, Hutchinson, Jerauld, Kingsbury, Marshall, Miner, Sanborn, Spink, Walworth.

Across those 24 counties combined, the non-special-needs Medicare Advantage and Cost plan listings fall from 304 in 2026 to 160 for 2027 (one listing per plan per county). Aetna isn't the only reason for the drop; Wellmark's exit, covered below, is a big part of it.

The 24 counties, one row each

Carriers are the companies with non-special-needs Medicare Advantage or Cost plans in the county. Plan counts leave out special needs plans, which only certain people can join. The last column counts 2027 plans listed at a $0 monthly premium.

Source: CMS CY2026 Medicare Advantage Landscape (September 2026 release) and CMS CY2027 Medicare Advantage Landscape (September 2026 release), South Dakota rows, non-special-needs plans. Plan years 2026 and 2027.

Three things stand out. First, no county is left empty: the thinnest have 5 plans for 2027 and the fullest have 9. Second, in 4 counties (Brule, Buffalo, Gregory, Jerauld) none of the 2027 plans is listed at a $0 premium; every option there is a Medica Cost plan. Third, Medica is in all 24 counties for 2027, and UnitedHealthcare and Sanford Health Plan are in many of them. That isn't a recommendation of any carrier; it's simply who filed plans with CMS for those counties.

What's still offered in each county for 2027

Here is every non-special-needs plan CMS lists for 2027 in each of the 24 counties. Premiums and out-of-pocket maximums are as the landscape file shows them; "n/a" means the file lists no amount in that column (for example, no total premium on a plan without drug coverage). Open your county to see its list.

Source: CMS CY2027 Medicare Advantage Landscape (September 2026 release), South Dakota rows, plan year 2027. A plan being listed here does not mean we offer it or that it fits you.

If you're in Sioux Falls: Aetna's 2027 plans

Aetna stays in Minnehaha and Lincoln counties, so Sioux Falls, Brandon, Harrisburg and Tea still have Aetna Medicare Advantage plans for 2027. But the lineup changes. Aetna's five 2026 plans (contract H1608) carry the word "Classic" in their 2027 names, and a new contract, H5521, adds three plans that use the old names. Here are all 8 Aetna plans in the landscape file for 2027. Each is offered in the same 10 counties.

Source: CMS CY2027 Medicare Advantage Landscape (September 2026 release), South Dakota rows. Premiums shown are the Minnehaha County listings; D-SNP premiums aren't in our non-special-needs extract. Plan year 2027.

Two plans with nearly the same name on two different contracts can have different networks, drug lists and costs. If your ANOC says you're moving to a "Classic" plan, compare it to the H5521 plan with the similar name before assuming they're the same. Our Medicare & You 2027 guide for South Dakota covers the rest of what's changing statewide.

Wellmark is leaving too

Aetna isn't the only carrier pulling back. The CMS CY2027 landscape shows no Wellmark Blue Medicare Advantage plans anywhere in South Dakota for 2027, after Wellmark filed plans in 43 counties for 2026. 18 of the 24 counties Aetna leaves also lose Wellmark, so a lot of households there will see two carriers disappear from the list at once. We cover that in detail in our Wellmark 2027 guide.

Your windows and your rights

You have two paths: join a different Medicare Advantage plan, or go to Original Medicare (with a Part D drug plan and, if you want one, a Medigap supplement). The timing looks like this:

Sources: Medicare.gov — Joining a health or drug plan; Medicare.gov — Special Enrollment Periods; CMS Publication 11219 — Understanding Medicare Advantage & Medicare Drug Plan Enrollment Periods; CMS Publication 02110 — Choosing a Medigap Policy.

A note on which rule fits your situation. Aetna isn't ending its Medicare contract; it's dropping counties. Federal rule 42 CFR § 422.62(b)(1) gives you a special election period when a plan is "discontinued" in the area where you live, not just when the whole contract ends. The notice Aetna mails you will spell out your exact dates. Use those. If anything in it doesn't match what you read here, go with the letter and ask us to look at it with you.

On Medigap: CMS Publication 02110 lists "your plan stops giving care in your area" as a guaranteed-issue situation. You can apply as early as 60 days before your Aetna coverage ends, and no more than 63 days after. The right only applies if you switch to Original Medicare rather than join another Advantage plan. Plans C and F are only available if you were eligible for Medicare before January 1, 2020; everyone else can use Plan D or G instead. Our plan non-renewal guide walks through the Medigap side step by step.

What doing nothing costs

If you don't pick anything, you end up in Original Medicare when your Aetna plan ends, with no drug plan. CMS Publication 11219 says it plainly: "You'll be enrolled in Original Medicare if you don't join another Medicare Advantage Plan before your current plan ends."

Original Medicare alone has no drug coverage and no supplement. The same publication explains the Part D late enrollment penalty: if you go 63 or more days in a row without Medicare drug coverage or other creditable drug coverage, a penalty can be permanently added to your Part D premium when you do sign up. That's the real cost of letting this slide: a drug gap in January, and a penalty that can follow you afterward.

What to do this fall

1. Find your county in the table above. If it's one of the 24, your Aetna plan isn't offered there in 2027.
2. Open every letter from Aetna. Your notice has your exact dates and, if you're in one of the 10 counties, the plan you're being moved to.
3. Make a list of your doctors and prescriptions. That's what separates the plans still offered in your county.
4. Decide between Medicare Advantage and Original Medicare on purpose. The Medigap guaranteed-issue right only helps if you choose Original Medicare.
5. Act by December 7 if you can. A choice made during Open Enrollment starts January 1 with no gap. The December 8 to February window is a backstop, not the plan.

Aetna leaving your county doesn't take your Medicare away. It takes away the option of not deciding.

How we help

Big Sioux Benefits is a licensed independent insurance agency in Sioux Falls. When a carrier leaves a county, we sit down with the people affected, look at the plans we offer in that county, and check them against your doctors and drugs. It costs you nothing to talk; carriers pay the agency. And we'll tell you plainly which of the plans we offer fit, and which don't.

You can absolutely do this yourself on Medicare's Plan Finder. Most people find the drug list is the part they want a second pair of eyes on. If you'd rather have someone local walk through it, book a conversation.

How we know all this: Big Sioux Benefits runs every article through a data desk that reads primary sources directly. For this one: the CMS CY2026 and CY2027 Medicare Advantage landscape files (September 2026 releases), South Dakota rows, compared county by county; Medicare.gov's Special Enrollment Periods and Joining a Plan pages; CMS Publications 11219 and 02110; and 42 CFR § 422.62, built by Strategic AI Architects. This is education, not advice. Big Sioux Benefits is a licensed independent insurance agency and is not connected with or endorsed by the United States government or the federal Medicare program. We take no payment from any carrier to feature a plan.