Doug, Doris and Kim gave you some really good answers. There is, however, one more factor to consider.
There have been distress sales and even a few foreclosures in your area of Great Falls. The tax assessors, by law, are required to take these into account when determining property values for tax purposes in a neighborhood. These sales, for all sorts of reasons, are, on average, at least 20% below market value.
This is why, Doug, the average regular sale price can go up in a neighborhood, while the assessed values for tax purposes can go down at the same time. Again, Doris is right to say that tax assessed values typically lag the regular sale market by at least 12 months. Hope this helps. I am available for a comprehensive market value analysis, if desired.