2026-09-10 · Illinois · Compliance

What is happening. A growing number of Illinois municipalities fund stormwater work through impervious-surface utility fees rather than property taxes. That is the mechanism by which community associations get billed for common-area parking lots, private drives and roofs — surfaces that generate no water-utility revenue and were historically unbilled.¹

The rates, verified

Wilmette (Cook County). One Equivalent Runoff Unit = 3,590 square feet. Single-family 2026 tiers:

• Tier 1 (under 3,000 sq ft impervious): $215/year, billed $53.75/quarter
• Tier 2 (3,000–4,300 sq ft): $265/year, $66.25/quarter
• Tier 3 (over 4,300 sq ft): $345/year, $86.25/quarter

But multi-family and non-residential parcels — the category that captures HOA and condominium common-area parcels — are charged by formula: (impervious surface area ÷ 1 ERU) × $155 ERU rate + $65 fixed fee.

Champaign. Rates set January 1, 2025 through December 31, 2026: single-family Tier 1 (500–6,000 sq ft) $6.07/month; Tier 2 (6,001–8,000) $12.96/month; Tier 3 (over 8,000) $16.78/month; all other property types $6.45 per ERU per month.

Decatur. One ERU = 4,500 sq ft; residential parcels of one acre or less $5 base + $1.10 ERU fee per month; non-residential $5 base + $1.10 × ERUs per month.

Wheaton, Peoria and Western Springs also operate stormwater utilities.

Why the formula matters more than the rate

1. Village of Wilmette, stormwater utility rates, ERU definition and multi-family formula ↩
2. Metropolitan Water Reclamation District, Watershed Management Ordinance and the detention/volume control trading program ↩