Decatur forms the bottom point of a 90-mile wide, 40-mile-tall diamond formed by Springfield to the west, Bloomington-Normal to the north, and Champaign-Urbana to the east. Common to the area, agriculture dominates the commercial activity and the local landscape. Agricultural processing giant Archer Daniels Midland has its headquarters in Decatur, and Caterpillar and agricultural processor Tate & Lyle also operate large plants.

Cost of living and home prices especially are among the lowest in the region and the U.S., and as measured by the Home Price Ratio, home prices are a bargain relative to local incomes. The crime rate, high for the region, bears watching. The city is fairly plain and doesn’t offer much in terms of entertainment or cultural amenities, but it does have a historic district with a mix of older homes, including some designed by Frank Lloyd Wright, and some Abraham Lincoln and Civil War sites.

The terrain is level and agricultural. Climate is typical continental with warm summers, fairly cold winters, and sharp seasonal changes. Considerable variation takes place within seasons. Summers are typically warm and humid with periods of mainly afternoon showers and thundershowers, and a few cooler, drier spells. Precipitation is more or less evenly distributed through the year. Spring and fall are typical for the region, with windy, changeable springs and relatively calm autumns with periods of warm, dry Indian summers. First freeze is mid-October, last is mid-April.