Complex sentence: Also being on the border, Lemmon hoped to hold a dual county seat in Perkins County, South Dakota and Adams County, North Dakota, that never happened, but it is now the largest city in present-day Perkins County.
Split into simpler sentences: Also being on the border, Lemmon hoped to hold a dual county seat in Perkins County, South Dakota and Adams County, North Dakota. The dual seat never happened, but Lemmon is the largest city in present-day Perkins County.