Are you talking from a stylistic point of view or what? Farm style houses, southern plantation homes, etc are all homes you are likely to find on a farm. These homes have large, often wraparound porches, and are generally larger in size. Many have gable roofs and wooden siding. In older suburban areas, you are likely to find ranch style, victorians, craftsman bungalows, and homes of brick construction rather than wood.
The spatial characteristics surrounding the home will likely give you a lot of important clues, as North Beach Person mentioned. Is it actually on a farm? Are there other homes in close proximity? Is the house close to the street? Property size? Farm houses are often widely spaced, surrounded by lots of land, while your typical old house would be found in small towns, or older low density areas of bigger towns and cities. They are generally much closer together.
Here are a few examples of old houses that are not farm houses in the geographical area you specified.
Kansas City
Kansas City #2
Omaha
Here are a few examples of farm houses in the area you specified.
Ste Genevieve, MO
Council Bluffs, Iowa
Treynor, Iowa
Glenwood, Iowa - This example is particularly interesting as it is visually similar to the more urban houses i showed above, which shows that sometimes its more of the home's farm setting that differentiates it as a farm house, and there are often a lot of nuances involved.
These obviously arent necessarily the best examples, these are the simply the best ones i came across while exploring these areas on google maps. But they do give you a good foundational idea as to the spatial and material differences that key the two "types" of old homes you mentioned in the areas you mentioned.