This county is situated in the northern part of the State, and in the Upper Wabash Valley. It has an area of 384 square miles, and, in 1870, had a population of 21,052.

A number of streams traverse the county from east to west in their general course. Of these, Eel River drains the northern part, the Wabash flows through the center, Deer and Pipe Creeks through the southern part. The Mississinewa, after entering the county, flows in a northwesterly direction for about seven miles, and empties into the Wabash about two miles above Peru. Besides these, there are numerous smaller streams emptying into one or the other of the above, draining every part of the county. There is, in consequence, and unusually large amount of fertile bottomland to be found. The country is rolling in many places, but not so broken as to at all interfere with early cultivation. There is considerable level country found, also, particularly between the streams, and on the dives, or tableland. Some oak openings, or "barrens," are found in the north, but the county, as a rule, was heavily timbered. Oak, walnut, ash, hickory, maple and other valuable timber was very plentiful when the county was first settled, and is still an item of no small value.

The rocks found exposed over the county belong to the upper Silurian age of the geologist. They seem to be the equivalents of the overlying limestone and the silico-magnesian limestone found further west on the Wabash.

Valuable building stone is obtained on the Mississinewa, near Brouillette's, and in the pool of the Peoria milldam, but neither places have been as extensively worked as they will be at some future time. Near the mouth of the Mississinewa are found beds of rock also suitable for building, and having an exposure of a mile along the river. Stone is also quarried west of Peru and in other places for building purposes, but is used mostly in foundations. The higher seam of limestone is used for burning into lime, and makes a strong and almost hydraulic cement. It is used both for home purposes and exportation.

The "Pillared rocks," some three miles east of Peru, on the Mississinewa, have been formed into numerous fantastic and picturesque shapes by the action of the waters. Here the precipitous walk of stone along the rive may be seen carved into pillars, chambers, buttresses and alcoves. Above, the rocks are covered with a growth of cedars, and the place is a favorite resort for picnic parties.

Miami County is well supplied with railways, being traversed from east to west by the Detroit, Eel River & Illinois, the Toledo, Wabash & Western, and the Chicago division of the Pittsburgh, Cincinnati & St. Louis Railway. The Indianapolis, Peru & Chicago runs through the county from north to south. This line was begun from Peru to Indianapolis, through surveys, in 1847, and completed to Peru August 17, 1854, being the first railway in the county. The next was the T.,W.&W., completed in 1856.