Mason County Electric Aggregation
Mason County’s municipal electric aggregation buys electricity from Constellation NewEnergy, Inc. at 11.538¢ per kWh, fixed through May 31, 2027. That’s 1.1¢ above Ameren’s current price to compare of 10.441¢.
How Mason County’s Rate Compares With Ameren
Mason County’s 11.538¢ rate is 1.1¢ above Ameren’s price to compare of 10.441¢ for the first 800 kWh a month (8.262¢ above that), which applies from Oct 1, 2026 through May 31, 2027. On 1,000 kWh in a month, that’s about $15.33 more for supply.
| Supply price | Per kWh | On 1,000 kWh |
|---|---|---|
| Mason County aggregation (Constellation NewEnergy, Inc.) | 11.538¢ | $115.38 |
| Ameren Illinois price to compare | 10.441¢* | $100.05 |
| Difference | +1.1¢ | +$15.33 |
* Ameren’s price is 10.441¢ for the first 800 kWh a month and 8.262¢ after that; the 1,000 kWh figure uses both.
Ameren’s price to compare changes several times a year. It was 11.326¢ from June 1 to September 30, 2026, when Mason County’s rate was 0.21¢ above it. Among the 260 fixed-rate aggregation programs in Ameren Illinois territory, Mason County’s is the 105th lowest.
These are supply prices only. Ameren Illinois still delivers the power and bills its delivery charges either way.
About Mason County’s Program
Constellation NewEnergy, Inc. supplies 30 of the 418 active Illinois aggregation programs, at a median fixed rate of 11.695¢.
| Community | City of Mason County, Mason County |
| Households | 5,781 occupied homes (Census 2020-2024 ACS 5-year) |
| Supplier | Constellation NewEnergy, Inc. |
| Delivery utility | Ameren Illinois |
| Contract ends | May 31, 2027 |
| Enrollment | Opt-out: residents are enrolled unless they return the opt-out notice |
| Referendum | March 2012 |
| ICC list entry | “Mason County | Constellation NewEnergy, Inc. | 11.538 | May 31, 2027” |
How to Opt Out or Leave
Illinois rules are the same in every aggregation community. In the Illinois Commerce Commission’s words:
- Opting out. “The chosen supplier will send opt-out notices to all residents and eligible small businesses within the municipality or county. You will need to fill out and return the opt-out notice in order to be excluded from the aggregation program.”
- Leaving later. “Suppliers are prohibited from applying early termination fees or penalties to residential and small commercial retail customers who terminate their contracts and switch to a different supplier or go back to the utility's service.”
- If you already buy from a supplier. “If you are enrolled with a supplier or the utility's residential real-time program at the time the opt-out notices are being sent out, you will likely not be included in your municipality's or county's aggregation program.”
Source: Municipal Aggregation, Plug In Illinois (Illinois Commerce Commission). More on how Illinois aggregation works on the Illinois aggregation page.
Other Aggregation Programs in Mason County
7 other Mason County communities have an active aggregation program, cheapest first.
| Community | Supplier | Rate | vs. default | Ends |
|---|---|---|---|---|
| Easton | Constellation NewEnergy, Inc. | 11.538¢ | +1.1¢ | May 2027 |
| Forest City | Constellation NewEnergy, Inc. | 11.538¢ | +1.1¢ | May 2027 |
| Havana | Constellation NewEnergy, Inc. | 11.538¢ | +1.1¢ | May 2027 |
| Kilbourne | Constellation NewEnergy, Inc. | 11.538¢ | +1.1¢ | May 2027 |
| Manito | Constellation NewEnergy, Inc. | 11.538¢ | +1.1¢ | May 2027 |
| Topeka | Constellation NewEnergy, Inc. | 11.538¢ | +1.1¢ | May 2027 |
| San Jose | Homefield Energy | 13.29¢ | +2.85¢ | Jun 2027 |
Frequently Asked Questions
Who supplies electricity in Mason County’s aggregation program?
Constellation NewEnergy, Inc., under a contract that runs through May 31, 2027, according to the Illinois Commerce Commission’s municipal aggregation list (checked November 2, 2026). Ameren Illinois still delivers the power.
What is Mason County’s electric aggregation rate?
11.538¢ per kWh, fixed until May 31, 2027. That is the supply price only; Ameren Illinois’s delivery charges are billed separately on the same bill.
Is Mason County’s aggregation rate lower than Ameren’s?
No. Mason County’s 11.538¢ rate is 1.1¢ above Ameren’s price to compare of 10.441¢ for the first 800 kWh a month (8.262¢ above that), which applies from Oct 1, 2026 through May 31, 2027. Ameren’s price was 11.326¢ from Jun 1 to Sep 30, 2026, when Mason County’s rate was 0.21¢ above it.
How do I opt out of Mason County’s electric aggregation?
Return the opt-out notice. The Illinois Commerce Commission says: “The chosen supplier will send opt-out notices to all residents and eligible small businesses within the municipality or county. You will need to fill out and return the opt-out notice in order to be excluded from the aggregation program.”
Is there a fee to leave Mason County’s aggregation program?
No. The Illinois Commerce Commission says: “Suppliers are prohibited from applying early termination fees or penalties to residential and small commercial retail customers who terminate their contracts and switch to a different supplier or go back to the utility's service.”
When did Mason County approve electric aggregation?
The ICC list gives Mason County’s aggregation referendum date as March 2012. In Illinois, an opt-out program needs voters to approve it in a referendum.
Sources
- Municipal Aggregation List, Plug In Illinois (Illinois Commerce Commission), checked November 2, 2026: supplier, rate, contract end and referendum date.
- Price to Compare - Ameren Illinois | Plug In Illinois (Illinois Commerce Commission): the current price to compare, effective October 1, 2026.
- Historical prices to compare, Plug In Illinois (ICC): Ameren’s earlier prices.
- Municipal Aggregation, Plug In Illinois (Illinois Commerce Commission): opt-out and early-exit rules.
- U.S. Census Bureau, American Community Survey 2020-2024 ACS 5-year estimates, table B25002: occupied homes.
