At that time, the successor Jefferson County was permanently created, taking its name from its predecessor and incorporating the heart of its territory.
In July 1858, gold was discovered along the South Platte River in Arapahoe County, Kansas Territory.
Its boundaries were set in Chapter X of the General Acts of the Territory of Jefferson which declared: That the territory comprised within the following limits, be erected into a county to be called Jefferson: commencing at a point on the 40th parallel of north latitude where it is crossed by the main channel of the south fork of the Platte River, thence up the main channel of said stream to the mouth of Clear Creek, to the mouth of Ralston's Creek; thence in a straight line to the point where the main channel of Montana Creek joins the south fork of the Platte, thence up said river to the mouth of the canon at the base of the mountains; thence west eight miles; thence north to where said line would intersect the south line of Jackson county; thence east to the south east corner of said Jackson county, thence north to the 40th parallel, thence east to the place of beginning.The Jefferson Territorial legislature after much debate designated Arapahoe City the county seat of Jefferson County.
However, the decision of the county seat was ultimately left to its people, and elections were held to determine what city would lead.
Its first town, Arapahoe City was organized in 1858 along Clear Creek just east of North Table Mountain.
Being an extra-legal government led some to actively question Jefferson County's legitimacy, and in early 1861 the citizens of the Junction, Mt.
Vernon and Bergen precincts voted to secede and, ironically, form their own extra-legal Ni Wot County in protest.
Vernon to secede on their own and create a real town at Apex, and relocate Jefferson Territorial functions there.