Larimer County, CO Environmental Rules: Flood Zones (2026)

Larimer County joined the FEMA National Flood Insurance Program in 1974. Floodplain regulations are codified in Article 12 of the Larimer County Land Use Code (effective June 1, 2023) and administered by Larimer County Engineering. The county recognizes five regulated floodplain types: the FEMA-mapped Floodplain (Zones A, AE, AO, AH, and floodway), the Best Available Floodplain (using updated studies like the Colorado Hazard Mapping Program post-2013-flood Big Thompson maps), Municipal Floodplain mapping forwarded by cities, the Poudre Growth Management Area Floodplain coordinated with Fort Collins, and County Flood-Prone Areas. A Floodplain Development Permit (FDP) is required before construction begins for any 'development' in the Floodplain Protection District - including new structures, substantial improvements, fill, grading, stockpiling, and storage of materials. New buildings in the regulatory floodway are prohibited, and substantial improvements to existing floodway structures are heavily restricted. The 'substantial improvement' threshold is the NFIP standard of 50% of the structure's pre-improvement market value, triggering full floodplain compliance. Colorado Water Conservation Board rule 2 CCR 408-1 requires at least 1 foot of freeboard above base flood elevation for residential structures statewide; Larimer County enforces this minimum. The Big Thompson River corridor was reshaped by the catastrophic 1976 Big Thompson Canyon flood (one of the deadliest in Colorado history) and the September 2013 floods, which prompted new CHAMP-based maps. The Cache la Poudre River corridor through Fort Collins is also high-risk. Applications and questions go to Larimer County Engineering at 970-498-5700.