American runners use miles. Speed is "mile pace" (minutes per mile). Daily runs are measured in miles and so on.
A marathon is the "26.2" (i.e. miles).
Interestingly, (continental) European runners do in fact use miles. It seems to be not unheard of, at least. I've seen miles used by Germans in online forums. E.g. citing daily mileage or minutes per mile pace.
Because many popular distances are metric, North American runners who use miles may still be mentally tuned to the metric side of things. For instance, someone mostly focused on miles in a marathon might take a note of their 10 km split time, checking whether it's properly below their 10 km race pace.
