For a mini Japanese lesson, the 人 character is a counter for people. So 6131人 means 6,131 people in that area are fans.
万 represents 10,000. In the West, we separate numbers every 3 places. For example, one million is written as 1,000,000. In Japan, numbers are separated every 4 places. If you look in the southernmost region in TheTanStar's image, the fan count is 1万0884人. This means 10,884 fans.
So you want to get 10万0000人 in a region for 100k fans.
(Towards the top of the image is 3万3727人 which is the total fans you have across the nation.)