The oldest continually operating marathon is the Boston Marathon.  The 123rd running of the Boston Marathon took place this on Monday, April 15.

This map indicates cooler climates host more marathons than warmer climates on a per-capita basis. The number of marathon race finishers across the nation has steadily grown over the past 40 years.  Since 1976 the number of race finishers has grown from 25,000 to over a half million in 2018.