According to information sent to me by a Delaware County resident, what was Big Rock Twp. now is part of Marion County. Big Rock was formed March 6, 1820 and was composed "of the territory north of the Indian line,lying north of Delaware,... attached to Bennington, Oxford, Marlborough, Radnor, Scioto and Union townships in that county." This territory became part of the new counties of Marion and Crawford. However, the name Big Rock does not exist today.