Major floods hit the County in June, 1975, May, 1981, February, 1996 and June, 2011 when Presidential Disaster Declarations were declared. The peak of the flood season is during May and June, which usually are the wettest months of the year, with June having the most rainfall. Rapid snow melt floods have occurred in February of 1985 and 1982 and March 2007.

The County has 30 floodplain maps for the Helena Valley along Spokane, Ten Mile, Prickly Pear and Silver Creeks, the Blackfoot River in Lincoln, Elk Creek in Augusta, Trout Creek near York and the Missouri River near Craig. These maps are available AT the Community Development and Planning Department, the Lewis and Clark County Library, and with the County Ombudsman. Floodplain mapping is driven by development,a history of flooding and cost, which means that much of the County is not mapped. Unmapped areas may be prone to flooding that occurs in established floodplains.

A floodplain ordinance regulates the identified floodplains. This allows residents to buy flood insurance through their local home owner's insurance agent. The County's floodplain management program has a Community Rating System rating of 8, which allows a 10% discount on flood insurance premiums. About 25% of flood losses occur for properties that are out of the floodplain, so flood insurance should be considered by the home owner near a floodplain.

Public disclosure of a property in the floodplain before a sale is required by law.

A permit is required before developing in the floodplain, which includes buildings, bridges, culverts, wells, fill or any alteration of the floodplain. Contact the Community Development and Planning Department for a permit application at 1 (406) 447-8374. For more information on floodplain management, go to the Department of Natural Resources and Conservation web site.