At their nearest, about 117 miles or 188 kilometres.
3 miles
About 158 kilometres or 99 miles.
From the city of Dublin to Knock in county Mayo is about 211 kilometres of 131 miles.
Mayo and Cork are both large counties. So it depends on where in each you are travelling between. They are at least 200 kilometres or 125 miles apart.
About 70 miles or 113 kilometres.
330 miles
If you mean St Johnston, in Donegal, just across the border at Derry, then you go via Limavady, Ballykelly, Eglinton, Derry city, heading out the Letterkenny road turning left approx 2 miles over the border.
There's a mountain called Croagh Patrick in County Mayo where, by legend, Patrick spent 40 days and nights fasting and praying for the conversion of Ireland to Christianity. There are ruins of a shack. As far as distance, I could only find that it took someone a little more than three hours to climb the steep mountain to the top. It is a beautiful place to see.
Fallbrook, CA is in San Diego County. It is very far north in the county and is only about 15 miles away from Temecula, CA which is in (southern) Riverside County.
20 miles
It s 13.09 miles according to MapQuest.
Rhode Power Station in County Offaly and Bellacorick in County Mayo were still active when i was in school, but as far as i know a lot of irelands peat resources are expended so they might be closing/have closed.