Question: What County that was incorporated on June 25, 1789 and named for John Hancock, has a short stream  from its source the river runs 5.4 mi south to its confluence with Mill Brook in Eastbrook?
Sentence (from "Little Bog River"): From its source ( ) in Osborn, the river runs 5.4 mi south to its confluence with Mill Brook in Eastbrook.
Relevant evidence: Yes