A week -- at my sister's in NJ during Hurricane Sandy. It was a good thing she had a grill, a wood-burning stove and a fireplace, and a gas stove. As soon as she has the money, she's going to invest in a generator.
We had one lasting within a few minutes of 24 hours one Christmas - power went off shortly after the Turkey had warmed nicely in the oven
In '87 we had one lasting about a week, due to strong winds bringing down numerous trees on the line. Although we weren't that far out of town, we had woods on three sides which the power lines came straight through. IIRC there where 13 significant trees down along our driveway as well so it was a while before we could get a car or even a motorbike out.
Almost a week. Can't remember what year it was, storms with hurricane force hit several states south and came thru here where our trees etc. can't withstand that. Trees and branches took out so many power lines it took a week to get power lines back up. Power crews from other states came here to help get power back on. Cell towers were going down so I was glad I had a land line, at least I could talk to people besides the neighbors. No gas pumps were working, no way to get gas to go anywhere. Glad it was Sept. so not too hot and not too cold.
Most electric utilities sign a voluntary 'mutual aid agreement' for just such incidences. When a major outage strikes one area, nearby utility crews are sent in to expedite getting the lights back on.
We had big, big wind storm in 1992, which blew hundreds of oak tree limbs down in the area, which was called Oak Grove. We were without power for about three days I guess it was. At the time, the majority of older electric lines were above ground on poles; now, here, in another city, the majority of electric in lines are buried!
September, 2011 a powerful line of thunderstorms with a derecho blew through this part of Iowa.
Our county was declared a disaster area and I was without electricity for 3 days.