What would be the smallest political boundary?

Depending on the state it may be referred to by different terms. In many states the smallest political sub-division is known as a "township.

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"The smallest political division of every State in the Constitutional Republic known as the United States is the voter, yes each person over the age of 18 in every State is part of the political division of each State. This is important to understand, your voice is as important as any others, be it a beggar or a Governor. From this it goes to the town, city, county and finally state. From this it goes from the States to the Federal.