Canyon County, ID Accessory Structures: ADU Impact Fees (2026)

Canyon County Code Chapter 11, Article 4 codifies the Canyon Highway District No. 4 (CHD4) development impact fee, adopted by Ordinance 22-014 on July 20, 2022 under an intergovernmental agreement between the County and CHD4 authorized by Idaho Code section 67-8204A. Section 11-04-09 sets the fee schedule for the CHD4 Mid-Star Service Area, a defined area east of Interstate 84 and north of the Boise River plus specified sections south of the river. Under that schedule, an accessory dwelling unit is billed as its own residential land-use category at $1,581 per dwelling unit, distinct from the $5,050 charged for a single-family house or the $2,857 charged for low-rise multifamily housing.

The fee applies to new Development within the Service Area lying within unincorporated Canyon County; it does not reach ADUs built inside Caldwell, Nampa, Middleton, Greenleaf, Melba, Notus, Wilder, Parma or Star, each of which administers its own impact fee ordinance. Under section 11-03-11, the fee is payable to CHD4 before or at the time an access permit is issued if a building permit is required, or at the time construction commences if no building permit is needed. Section 11-03-23 entitles a fee payer to a refund if the building permit is denied or abandoned, or if CHD4 has not appropriated or begun construction of the funded system improvements within eight years (extendable to eleven years with written justification), plus interest at half the legal rate under Idaho Code section 28-22-104. Fees collected are restricted to system improvements benefiting the Mid-Star Service Area under the Capital Improvements Plan.