After verifying that the dew point sensor at the Moorhead Airport automated station was operating properly, it has been determined that the 88 degree F dew point temperature recorded from 7pm to 9pm July 19, 2011 is the Minnesota state record for highest dew point temperature. The previous dew point temperature record was 86 degrees F set at Pipestone and St. James on July 23, 2005.
Note: at the time the dew-point reached the record 88F, wind speeds were decreasing and the air temperature rising. This suggests there were local influences that helped drive the dew-point to this extreme level.
For the curious or technically inclined, an in depth investigation of the sensor at Moorhead can be seen here.
The Weather Underground posted research on the US and worldwide dew points in this blog.