Mifflin County was formed in 1789, taken from parts of Cumberland and Northumberland Counties. It was named in honor of Thomas Mifflin, the first governor of Pennsylvania. Many land and court documents pertaining to the first inhabitants of the area are found in Cumberland County.

Early records tell of two early paths or roads in use before the settlers came. An early Indian path known as the "Juniata Path" followed the Juniata River from Lewistown to Mount Union. It was used by the early traders and was called the "Traders Path" in the early land grants. Evidently it carried an increasing traffic, for a little later it was called the "Traders Road" or the "Great Road."

Another Indian path followed Jack's Creek from Lewistown to Middle Creek (Snyder County) the "War Path" or "Warriors Path." It was also called "Moghanoy Road." Middle Creek was once known as Moghanoy (or Mahanoy) Creek. These early paths were not laid out by surveyors but were made by decades of Indian travel. The court records of Cumberland County tell of five roads laid out before September 1789, when Mifflin County was formed. A petition for a sixth was never acted on.

Early roads were of varied width, and the names by which they were called tell of progressive improvements. First "bridle,” "wagon," “then "carriage" roads were laid out. Although the first settlements in Mifflin County were made in 1754, Indian wars prevented them from being permanent until 1765.

As early as 1731 traders had left written records of the Shawnee Indian village of Ohesson, ruled over by Chief Kishacoquillas, who was a firm supporter of the whites. Its site, since 1790, occupied by Lewistown, the county seat, remained an Indian center until the coming of Arthur Buchanan, a trader and the first settler, in 1754.

Scott Irish immigrants were the first settlers in the area. But in August of that year, Fort Granville, a British stockade, was burned and captured by a French and Native American force during the French and Indian War. Many of the settlers fled, but it was long before the Scotch-Irish came again, and during the Revolution, they were a safeguard on the frontier against the inroads of the British-backed Indians.

The most interesting records at Carlisle are the inventories of estates that show how the pioneers lived. The inventories include everything a man owned at his death, from a corner cupboard and "what is in it" to “old iron.”

A study was made of the seven earliest inventories from Mifflin County. They differ greatly, showing the relative wealth of the men. One man had an apprentice and four slaves. Certain items are standard: horses, cows, plows, axes, spinning wheels, beds, saddles, pots, and fireplace utensils. Some things sound strange today: Riddle (grain-sifter), froe (iron splitting tool, a frow), hatchel (instrument for cleansing flax), tackling (harness), snead (scythe handle).

Hogs and sheep are listed; one man had geese. Rye, wheat, Indian corn, hemp, grass, skins, yarn, clover seed, linen, feathers, tallow, boards, and leather were of value. Also listed were rifle, musket, gun, pistol, tomahawk, powder horn-still. cask, barrel, keg-wedge, mall rings, log chains-cart tire, horse gears, etc.

Men's apparel then in use included: coat and waistcoat, riding coat, greatcoat, hat, shoes, stockings, boots and spurs, knee buckles, buckskin breeches. Two of the men had silver watches.

Furniture pieces used included a bed, a dining table, a tea table, an iron stove, brass warming pan.

The housewife used such things as: (although all were listed as property of the husband) dough-tray, brass candlesticks, tablecloth, knives and forks, pewter, trenchers (wooden plate on which to carve or serve meat), bowls, pitcher, bottles, teapot, cups, saucers, spoons, bread baskets, pickling tub, earthenware, crock, cream jug, pails, churn tub, flat iron, smoothing iron, blankets, tea kettle, tongs, frying pan, skillet, griddle, spit (iron for holding meat while roasting), iron pots, crook, hooks, racks, fire irons, and punch bowl.

One man in Kishacoquillas Valley owned several things found in no other inventory: Coffee pot, tin cup, pepper box, nutmeg grind-er, porringer (howl for porridge), lantern, basin, trunk, looking glass, razor, quilt, bolster, Delft ware and a nursery of apple trees.

The first map to show anything of interest in what is now Mifflin County was the Lewis Evans map of 1749. Shade Mountain, the Juniata River, Jacks and Kishacoquillas Creeks and the Indian village, "Kishequokeles," are clearly marked. In 1759 Nicholas Scull made a map of Pennsylvania which shows Fort Granville about 1.9 miles above the mouth of Kishacoquillas Creek. Another map by W. Scull in 1770 locates Jack's Mountain, "Kikicocolas" Valley and Long Hollow. It was Reading Howell's 1792 map of Pennsylvania that first showed Mifflin County in detail: townships, roads, mountains, streams, mills, churches, and other important places.