Price per square foot only is useful when you are comparing similar homes or if you have an homogenous neighborhood...homes of similar style, age, amenities like you would find in a subdivision that has specific covenants and restrictions. There are 2500 sf homes worth millions, and there are 2500 sf homes worth $180,000 in Naperville. Where each is located, the size of the land, the style and construction materials used, the amenities in each home and many other factors all influence the overall value.
There is no way to average the all the homes together and have a reliable and meaningful cost per square foot figure. So, if you are selling a home, a market analysis of your home to determine the anticipated value will yield a fairly accurate average of price per square foot for your home. Similarly, if you are buying a home, a market anaylsis will determine if your purchase is above or below market value compared to similar homes.

Mom,
There is not really an answer to your question about an average square foot price. There are a lot of factors to determine pricing on homes, first off the square foot pricing is going to vary depending on what you are looking at. Interior features vary greatly, location is a factor, exterior amenities, single family vs. townhome, the list goes on and on. If you are a seller I recomend you have a Realtor perform a thourough Comparitive Market Analysis (CMA) to determine a selling price. If you are a buyer the same CMA can be used to come up with a homes value. Using price per square foot initially will only confuse you, but once you narrow down how you comparing homes it does start to make some sense but is not always the best way to look at a homes value.
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