ADU rules in Springfield, IL — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Springfield's zoning code expressly prohibits using any detached garage, accessory building, or structure as a dwelling unit, so a freestanding accessory dwelling unit (ADU) is not permitted under Zoning Ordinance Section 155.068(b)(2). Illinois has no statewide ADU law in force (HB 1813 remains pending), so the local ban governs.
Under the City of Springfield Code of Ordinances, Chapter 155 (Zoning), Section 155.068(b)(2), accessory structures in residential districts are limited to an 18-foot height and, critically, "in no case shall any portion of a detached garage, accessory building, or structure be used as a dwelling unit or for any business or office use." Because Springfield's zoning ordinance does not establish an accessory-dwelling-unit (ADU) category and affirmatively bars residential occupancy of detached accessory buildings, a backyard cottage, coach house, or garage apartment as a separate dwelling is not allowed by right. Springfield's minimum required lot area per dwelling unit (Section 155.056) and minimum lot width rules (Section 155.055) further constrain adding a second dwelling on a single lot. At the state level, Illinois has not enacted statewide ADU preemption: the proposed Local Accessory Dwelling Unit Act (HB 1813, 104th General Assembly) had only reached a second reading and was not signed into law as of mid-2026, so it does not override Springfield's local prohibition. Property owners seeking any residential second unit must pursue a zoning variance or text amendment through the Springfield Planning and Zoning Commission.
Using a detached garage or accessory building as a dwelling violates Section 155.068 of the Zoning Ordinance and is subject to the zoning penalty cross-referenced at Section 155.999, plus code-enforcement action requiring the unauthorized living space to be vacated, removed, or brought into a permitted use.
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See how Springfield's adu rules rules stack up against other locations.
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