These maps show generalized laws from 2013 for the ages at which operators/riders must wear a helmet when on a bicycle or motorcycle. There are a few exceptions and exemptions (see the data source), most of which relate to the requirement of wearing a helmet, regardless of age, when riding with an instructor’s permit.

Not surprisingly, the most lax laws tend to apply in the middle of the country, where the population density is lower. Iowa and Illinois are the only states with no helmet requirements for either bicycles or motorcycles. California has the strictest pair of laws: bicycle riders 17 and younger and all motorcycle riders must wear helmets.

Data source: http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/state_transportation_statistics/state_transportation_statistics_2012/html/table_02_05.html