You don't need multiprocessing. All you need to do is use a better algorithm.
>>> import collections
>>> import random
>>> import time
>>> def f():
... t = time.perf_counter()
... print(collections.Counter(random.randint(1,6) for _ in range(1000000)))
... print(time.perf_counter() - t)
...
>>> f()
Counter({2: 167071, 4: 166855, 3: 166681, 1: 166678, 5: 166590, 6: 166125})
2.207268591399186