An important object to keep in mind about ZIP code finder is that they change over time. In some cases these change can be quite amazing, but more frequently they are small and subtle. When a ZIP code changes its definition it does not change its name like a census zone. The ZIP code that was called '63301' in St. Charles County, Mo in 1985 has since been broken into first two and now three ZIP codes. These new codes were not called 63301.01, 63301.02 and 63301.03; they were called 63301, 63303 and 63304. So what is referred to as 63301 today represent about a third of the area that it referred to in 1985. The new code 63303 did not exist 12 years ago and it has already changed its definition so that it now represents about partially of the area it included whRead more...Link