There is no hard fast rule to answer this question. A group can be as large or as small as they choose. As a recommendation, we suggest a group should not be larger than 100 dwelling units. This allows for each block captain to have roughly 10 homes assigned to them. Again, this is simply a suggestion to help mitigate a work load that is too large to manage.
Can a group be larger? Certainly, the city has successful groups as large as 500 homes and as small as 12 homes. It all depends on the dedication of the groups leadership.