Lake County, IL Environmental Rules: Stormwater Management (2026)
Key Facts
- Governing law
- Lake County Code § 151.197
- Storm sewer design storm
- 10-year frequency minimum
- Minimum storm sewer diameter
- 12 inches
- Detention outlet requirement
- Anti-seep collars required
- Applies to
- Unincorporated Lake County only
Summary
New subdivisions in unincorporated Lake County must meet the county's stormwater management facility standards, sizing storm sewers for a ten-year storm and following detention-basin design rules the Public Works Department enforces.
(C) Outside the right-of-way. (1) Storm sewer facilities. ... The storm sewer system shall be of sufficient capacity to carry the discharge for a storm of ten-year frequency. Depending on site characteristics, a greater frequency design may be required. Storm sewer capacity calculations shall be required. ... All storm sewers shall be at least 12 inches in diameter. ... All stormwater detention basin outlet pipes shall be equipped with anti-seep collars.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: 2026 S-15: Supplement contains: Local legislation current through Ord. 26-0618, passed 6-9-2026 | State legislation current through ILCS Pamphlet 2025 #5).
Full Breakdown
Lake County Code § 151.197, part of the Unified Development Ordinance's subdivision regulations, sets engineering standards for stormwater facilities built with new development: storm sewers must carry a ten-year-frequency storm, be at least 12 inches in diameter, and detention basin outlet pipes must have anti-seep collars. The Director can modify standards case-by-case. This chapter applies only to unincorporated Lake County (§ 151.003). Waukegan, North Chicago, Highland Park, Gurnee and Libertyville enforce their own stormwater codes for development inside city limits.
Violations & Fines
No penalty specific to this section; violating any provision of the county code carries a fine up to $1,000 per offense, with each day of continued violation a separate offense (§ 10.99).
Frequently Asked Questions
Does this apply inside Waukegan or Highland Park?
What size must new storm sewers be in a county subdivision?
Sources & Official References
Other rules in Lake County
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