Mark Twain is often quoted (rightly or wrongly) as saying, "There are lies, damned lies, and statistics." Depending on how you pull the statistics, an argument can be made that prices in Evanston either rose, fell, or were stable over the last year.
I answer from the perspective of someone who is very analytical and closely tracks the Evanston and surrounding marketplaces (Skokie, Wilmette, Glenview, Rogers Park (east and west)) and who participates in gathering statistical data for Morgan Stanley's research deparment for the broader Chicagoland area.
My answer assumes you refer to price when you speak of decline. There are other interpretations to your question - and it's unclear which meaning you seek an answer to.
In that regard, I agree with Alan and Noah, who - like me - reguarly work the Evanston marketplace. They are correct Evanston is a dynamic, vibrant market, that has not escaped the overall trends of the past couple years, but which also hasn't suffered as much as surrounding communities - because it remains a destination marketplace thanks to the University, the proximity to the lakefront, and the presence of the commuter trains (el and Metra.) As a diverse community with regard to its housing stock (styles, ages, and types) and the accompanying lifestyles for that housing stock (condo living being different than living in a house, for example), some areas have fared more poorly than others.
In general, over the past rolling 12 months, prices have been stable to modestly up for both houses and condos, with the recovery hitting houses earlier than condos. However, the number of deals is still down substantially (30 to 40%) and market times appear to have stabilized.
Realize the pricing picture depends to a large extent on market composition, to borrow an economics phrase. When as a percentage of deals, most of the sales are distressed properties, the average price will show big drops because generally the distressed deals are steeply discounted, pulling the average down disproportionately. When there is more normal activity occuring - and the market mix better matched to historical norms -- prices rise from the distressed level, on the average. This doesn't mean the value of a particular property rose or fell in its instrinsic value, it means the type and number of properties comprising the average has deviated from its normal mix.
In the go-go years of lots of new construction, the phenomonen was seen in a different way. It appeared prices were going up 20% a year simply because a lot of new construction inventory was added to the marketplace. It didn't mean the value of a vintage condo necessarily went up 20% in a year. It meant the average of condo sales shifted in response to a change in the relative number of new and old properties in the average.
The value of a particular property is subject to what a buyer is willing to pay and a seller is willing to sell for.
There remain more sellers who want to sell than buyers who want to buy - so prices will be under presssure until there is better balance in the marketplace between buyers and sellers. You need to segment the market between condos, co-ops, and houses - because they are all very different markets, just as the dynamics for the vintage market is different than the new construction market.
Evanston has fared far better than its neighbors in Rogers Park, Skokie, and Glenview - for different reasons in each community. Wilmette, for houses, has so far outperformed Evanston. It has a limited condo marketplace, so it's difficult to compare on that front.
Feel free to be in touch with me to discuss the specifics behind your question.