A B737 flight crew suffered an taxiway incursion in CLT when they failed to hold short of taxiway E-11 as cleared.

Narrative

Ground Control told us to taxi north on E; hold short of E11. I made a note of it; but the Captain and I misread the airport diagram. The intersections are not in numerical order; so instead of E9; E10; E11; they are E11; E9; E10. Still; that's no excuse; and by the time we recognized the mistake; we had taxied past E11. Captain immediately stopped the aircraft and notified Ground Control. He also apologized to them. They were very understanding and told us to continue taxiing on E to Runway 18C. We both misread the taxi diagram. Also; was fairly congested and we missed the E11 sign. Also; as stated earlier; intersections are not in numerical order; and we incorrectly assumed that they were. (E11 came before E9 and E10). Also; I momentarily had to go heads down as I finished inputting weight and balance in the FMS. Was a fairly high workload situation at the end of a 4 leg; 12 hour day. In the future; we both need to be much more vigilant in reading airport diagrams; slow down; and realize that we prone to mistakes at the end of a long day and a 4 day trip.