The entire premise of the series is that the civilization of the Twelve Colonies has been attacked and the Battlestar Galactica is protecting a fleet of approximately 50,000 survivors of all the colonies.
Direct reference is made to attacks on some of the colonies, from the pilot episode:
Adama: (over the intercom) Preliminary reports indicate a thermonuclear device in the fifty-megaton range was detonated over Caprica City thirty minutes ago. Nuclear detonations have been reported on the planets Aerlon, Picon, Saggitarion and Geminon. No reports on casualties, but they will be high.
So this is directly referencing five of the colonies having reports of attacks.
At the end of the miniseries Adama addresses the survivors at a ceremony on Galactica:
Adama: Are they the lucky ones? That's what you're thinking, isn't it? We're a long way from home. We've jumped way beyond the red line, into unchartered space. Limited supplies, limited fuel. No allies, and now, no hope? Maybe it would have been better for us to have died quickly, back on the Colonies with our families, instead of dying out here slowly, in the emptiness of dark space. Where shall we go? What shall we do? Life here began out there. Those are the first words of the sacred scrolls, and they were told to us by the Lords of Kobol, many countless centuries ago. And they made it perfectly clear that we are not alone in this universe. Elosha, there's a thirteenth colony of humankind, is there not?
I think it is fairly clear that the implication is that all twelve colonies were attacked and destroyed. This is reinforced by the fact that the council of the colonies is re-formed with representatives drawn from the survivors in the fleet, a representative from each of the former colonies.