Which Side of the Mystic River Has the Lower Tax Bill?

On the state's fiscal year 2027 mill rate list, the Mystic Fire District appears twice. Groton properties in the district are taxed at 2.76 mills. Stonington properties in the same district are taxed at 2.12 mills. It is one fire district, and its annual report says its taxes are collected through both the Groton and Stonington town halls.

Two rates for one district shows the main point about Mystic property taxes. A mill rate only means something next to the assessment it is multiplied by. Groton and Stonington build their assessments on different revaluation years, so their rates don't line up. Buyers comparing a house in West Mystic with one across the bridge often see the town rates first: 25.29 mills in Groton and 19.2 in Stonington for the fiscal year that started July 1, 2026. That 6-mill gap looks like a big reason to pick the east side. Measured against what homes actually sell for, the gap is much smaller.

The Same Assessment Means a Different House in Each Town

Start with the comparison most people make. Apply a $350,000 assessment to each town's FY2027 rate, listed in the Connecticut mill rate dataset. Groton's town tax comes to about $8,852 and Stonington's to $6,720. That is a difference of about $2,130 a year before any fire district charge.

That math assumes a $350,000 assessment means the same house in both towns, and it doesn't. Each year the state Office of Policy and Management compares assessments with actual sale prices in every town. For the 2024 grand list, its equalized grand list data put Groton's residential assessments at 45.02% of market value and Stonington's at 53.20%.

At those ratios, a $350,000 assessment in Groton matches a home worth roughly $777,000. In Stonington it matches roughly $658,000. The Groton house pays the higher rate, but it is also the more valuable house. Comparing the two rates directly ends up comparing two different homes.

What the Gap Looks Like Against Market Value

The fairer test is two homes with the same market value, one on each side. Multiply each town's rate by its residential ratio, and you get a rough tax rate per $1,000 of what a home is actually worth.

The posted gap is about 6.1 mills. Measured against market value, it is about 1.2 mills, or roughly $590 a year on a $500,000 home. Groton is still higher, but the difference is about a fifth of what the posted rates suggest.

The Mystic Fire District numbers shrink the same way. At the same ratios, the Groton-side rate of 2.76 mills comes to about $1.24 per $1,000 of market value. The Stonington-side rate of 2.12 comes to about $1.13.

These are illustrations, not bill estimates. The ratios come from 2024 grand list sales and the rates from fiscal 2027, and every property's assessment sits at its own point relative to its sale price. Treat the size of the gap as the useful part, not the exact dollar amounts.

Groton's Side of the Comparison Changes This Winter

The Groton side is the one about to move. Groton's last revaluation was in 2021, and Stonington's was in 2022. Connecticut requires towns to revalue every five years, so Groton's turn has come. The Day reported in April that Tyler Technologies is running the revaluation for the October 1, 2026 grand list. The new assessments will form the basis of Groton tax bills through 2031.

Groton's previous revaluation shows what can happen. In that same report, Groton Assessor Mary Gardner told The Day that the 2021 revaluation raised residential values about 30%, and the town's tax rate fell from 25.98 mills to 21.28 for the 2022-23 budget. She said towns generally lower the rate when the grand list rises, because the goal of a revaluation is to match the market, not to raise more revenue. She also expected residential and apartment values to rise again this time, citing apartment demand tied to the Electric Boat expansion.

For a buyer, this means the 25.29-mill rate on a Groton listing sheet won't last. It sits on assessments that are five years behind the market, which is why Groton's ratio was down at 45.02%. Once new values land, Groton's assessments should move closer to market value, and the town sets a new rate during its budget process. No rate has been announced, and the size of the value change hasn't been reported. The 6-mill gap on paper is likely to look very different a year from now, and the gap against market value is the one worth tracking.

Stonington isn't standing still either. The state's revaluation schedule lists its next revaluation for 2027. Its 2025 grand list grew 1.2%, which The Day noted is typical for a year without a revaluation. That revaluation will measure Stonington's assessments against the market again, so the east side's ratio will change too.

The Groton Revaluation Calendar, Step by Step

If you are buying on the west side this season, or already own there, these are the dates that matter:

1. November 2026. Groton's Assessment Division says proposed-value notices go out during November. Owners can call the number on the notice to set up a short informal hearing, which usually runs 10 to 15 minutes, and they get a second notice after the review.
2. The following February. According to The Day, owners then get another notice listing their assessment and any exemptions, along with their right to appeal to the Board of Assessment Appeals. The town's page still shows the deadlines from the previous cycle, so check it for the new dates once they are posted.
3. Fiscal 2028 bills. The state dataset pairs each grand list with the fiscal year that follows, so the 2025 list carries the FY2027 rates. By that pattern, the new October 1, 2026 assessments will meet a new rate in the fiscal year starting July 1, 2027.
4. 2027 on the east side. Stonington's revaluation follows, and that will change its own ratio.

Timing matters at closing. A Groton home that changes hands this winter may show one assessment on the listing, a different proposed value on a November notice, and a final figure in February.

Questions to Ask About a Specific Mystic Address

The town rate is only part of a Mystic tax bill, so the parcel itself decides the rest.

• Which town is it in? The river divides Mystic, but addresses near the water can be confusing. The assessor's records settle the question.
• Which fire district? The state lists both the Mystic Fire District and the Old Mystic Fire District in each town. Old Mystic is at 2.65 mills on both sides for FY2027. Groton's fire departments page says independent districts have their own boards and taxing power, and it tells owners to ask the district or the Planning Division which district covers a parcel.
• Which grand list is the listing's tax figure from? On the Groton side, a figure based on the 2025 list reflects 2021-era values.
• Has a revaluation notice arrived? If a Groton seller has received a November notice, the proposed value tells you more about the home's next few tax years than last year's bill does.

Quick Answers

Is the Stonington side of Mystic always cheaper to own? Based on the 2024 ratios and FY2027 rates, Stonington's town tax per dollar of market value comes out a little lower, by about 1.2 mills. That is much less than the posted rates suggest, and Groton's revaluation could change it.

Will Groton taxes go up after the revaluation? Groton's own Q&A says each owner's tax may rise or fall depending on how their property's value changed compared with the average change across town. The new rate won't be set until the budget process.

Why does a house's listed taxes differ from what I calculate? Listing figures usually come from the most recent bill, which uses the current assessment and the current rate. Exemptions, the fire district charge, and the timing of a new grand list can all make the next bill different.

This post is general information about how Connecticut towns assess and tax property. It is not tax, legal, or financial advice, so please confirm the details for your own property with the town assessor or a qualified tax professional.

If you're comparing homes on the two sides of the Mystic River and want help working out what a specific address's taxes are likely to be after the revaluation, Chris Maynard can go through the assessment, the fire district, and the timing with you before you make an offer. Let's Connect.