If you are using the ILA core in 14.1 or later with an 8-bit counter design, while in Single Trigger Run Mode, it is possible to see multiple trigger increments. The code example below increments "trig_count" by three on the rising edge of bit[7] instead of incrementing by one. This is a known issue that is scheduled to be fixed in a later version of the tools.
always @ (posedge clk)
begin
if(trigout)
trig_count <= trig_count + 8'b1;
end