A "--" in the district column means, that the town is a district-free town, i.e. it is by itself a district.
... family size is 2.91. In the village the population is spread out with 21.7% under the age of 18, 5.1% from 18 to 24, 32.6% from 25 to 44, 31.2% from 45 to 64, and ...