Almost all the salt we buy is iodized. Iodine was added to salt early the last century to provide iodine to people who were not getting enough, specifically in the upper northeast US. They were getting goiters, so the governement requested the salt companies to add Iodine salts to prevent them.
"When it rains, it pours" comes from a salt company advertisement, after they added something to prevent salt from clumping up in humid weather.
Thanks for allowing me to put this nugget of useless information somewhere for all eternity.
Grant