If you tracert'ed the target and then whois'ed all the hops in between you will see lots of different countries listed if the taget is abroad. You will also find some different countries listed if the tracert stays within the US. There is an English company that owns a large part of the fibre? backbone in the US so if you were to whois a router on that backbone you will see it listed as being owned by a British company.

If, as you claim, the attacker was on the same subnet then a tracert would have given you very little and the routers would not have routed the packets outside the subnet. With that in mind I really question whether that IP is anywhere close to your subnet - assuming of course that you are referring to a C Class network, (XXX.XXX.XXX.0/24). It would be quite possible for a B Class, (XXX.XXX.0.0/16) to be in another country and an A Class, (XXX.0.0.0/8) would almost certainly hop international boundaries. But then they wouldn't really be considered as being on _your_ subnet.

Do the first three octals of the IP address attacking you match the first three octals of your IP?