HERLEMAN
SubstationIllinois · AMEREN ILLINOIS COMPANY
At a glance
HERLEMAN is an electric transmission substation in Illinois, on AMEREN ILLINOIS COMPANY's transmission network. It is classified as high-voltage (345 kv) and connects 6 transmission lines. Substation proximity is one of the strongest speed-to-power signals for siting a datacenter — interconnection distance to an energized, high-voltage bus is often the binding constraint on time-to-energization.
Voltage & classification
Connected transmission lines
Lines terminating at or passing through this substation, by HIFLD line ID, highest voltage first.
| Line ID | Voltage | Owner | Status | Length |
|---|---|---|---|---|
| #162598 | 345 kV | — | IN SERVICE | 14.9 mi |
| #162609 | 345 kV | AMEREN ILLINOIS COMPANY | IN SERVICE | 46.6 mi |
| #162592 | 138 kV | AMEREN ILLINOIS COMPANY | IN SERVICE | 37.1 mi |
| #162593 | 138 kV | AMEREN ILLINOIS COMPANY | IN SERVICE | 2.4 mi |
| #162594 | 138 kV | AMEREN ILLINOIS COMPANY | IN SERVICE | 2.5 mi |
| #162597 | 138 kV | AMEREN ILLINOIS COMPANY | IN SERVICE | 15.0 mi |
Nearby datacenter candidate sites
Scored candidate sites within roughly 25 miles of HERLEMAN, ranked by DC Readiness. Sites this close to an energized substation carry a strong speed-to-power advantage.
| Site | Type | State | County | Voltage | Capacity | Queue wait | Score |
|---|---|---|---|---|---|---|---|
| PALMYRA | Substation-Adjacent | MO | Marion County | 345 kV | 600 MW | 3.9 yrs | 64.1 |
| MAYWOOD | Substation-Adjacent | MO | Marion County | 345 kV | 600 MW | 3.9 yrs | 64.0 |
| HERLEMAN | Substation-Adjacent | IL | Adams County | 345 kV | 600 MW | 4.8 yrs | 62.1 |
| OZ Adams | Greenfield | IL | Adams | — | — | 4.8 yrs | 59.9 |
| UNKNOWN117838 | Substation-Adjacent | MO | Ralls County | 161 kV | 100 MW | 3.9 yrs | 59.0 |
| OZ Marion | Greenfield | MO | Marion | — | — | 4.3 yrs | 58.9 |
| UNKNOWN120842 | Substation-Adjacent | MO | Ralls County | 161 kV | 100 MW | 3.9 yrs | 58.9 |
| UNKNOWN120975 | Substation-Adjacent | MO | Ralls County | 161 kV | 100 MW | 3.9 yrs | 58.6 |
How does HERLEMAN compare with other substations in Illinois?
Illinois has 1,986 substation records in HIFLD, of which 209 carry a station name; the rest are unnamed tap points, risers and line ends. 89 named substations in the state are in HERLEMAN's 345–499 kV band (43% of named stations). 3 sit in a higher band. 92 named substations in Illinois operate at 345 kV or above. The highest voltage recorded in the state is 765 kV, and the state median is 161 kV.
Who owns the transmission lines at HERLEMAN?
The 6 connected lines listed above are owned by AMEREN ILLINOIS COMPANY. Line voltages range from 138 kV to 345 kV. Their combined recorded length is about 118.3 miles.
How do candidate sites near HERLEMAN score?
The 8 highest-scoring candidate sites within about 25 miles range from 59 to 64 on the 0–100 DC Readiness scale. They fall in Marion County, Adams County, Adams, Ralls County. The Illinois average across 3,641 scored sites is 54.3. 795 of those Illinois sites are classed as substation sites (candidate locations generated at an existing substation).
Frequently asked questions
What voltage is HERLEMAN substation?
HERLEMAN has a maximum voltage of 345 kV and a minimum of 138 kV. That places it in the 345–499 kV band. The median named US substation in this dataset is 115 kV, so HERLEMAN is above the national midpoint.
How many transmission lines connect to HERLEMAN substation?
6 transmission lines terminate at or pass through HERLEMAN in the HIFLD line data. The connected lines listed here run at 345 kV, 138 kV. Together the listed lines cover about 118.3 miles.
Who owns HERLEMAN substation?
HIFLD does not publish substation owners directly. Most of the transmission lines that end at HERLEMAN belong to AMEREN ILLINOIS COMPANY. GridCensus derives this from the line data, so confirm ownership with the utility for anything contractual.
Where is HERLEMAN substation located?
HERLEMAN is in Illinois at 39.8785, -91.3567. The datacenter candidate sites closest to it are in Marion County, Adams County, Adams.
Are there datacenter candidate sites near HERLEMAN substation?
GridCensus lists at least 8 scored candidate sites within roughly 25 miles of HERLEMAN. The highest-scoring is PALMYRA at 64/100. Across Illinois, the average DC Readiness score is 54.3.
Other 345 kV substations in Illinois
- GOODINGS GROVE· 20 lines
- CAHOKIA· 19 lines
- ELECTRIC LIGHT 345 KV· 16 lines
- BURNHAM· 14 lines
- LOMBARD· 13 lines
- CHERRY VALLEY· 12 lines
- COMMONWEALTH EDISON DES PLAINES (345KV)· 12 lines
- EAST FRANKFORT· 12 lines
- All named substations in Illinois· 209 stations
- Datacenter candidate sites in Illinois· 3,641 sites
- Brownfield and retired plant sites in Illinois
- Substations by state
About this data
Source: HIFLD Electric Substations and Transmission Lines (U.S. Department of Homeland Security), as published June 29, 2026. See the methodology for how records are matched, cleaned and scored.
Cite as: GridCensus, “HERLEMAN substation, Illinois”, https://gridcensus.com/substations/illinois/herleman-76e0404f (data as of June 29, 2026).
Dataset updated . Screening estimates derived from public data sources.
Substation attributes are derived from public HIFLD / EIA infrastructure data and may lag real-world upgrades or retirements. Voltage and connected-line counts are screening figures — confirm available capacity and interconnection terms directly with the operating utility and ISO.
Go deeper than the public screen
Every site and score for HERLEMAN substation, Illinois is free to browse. Pro adds Watchtower on 25 sites, alerts when new candidate sites, datacenters or interconnection-queue requests appear in your markets, score and capacity history, and CSV export. Enterprise adds team seats, weekly data files for all 147,272 sites, the REST API and an MCP server for AI tools.