[Mike AA]

Lisa, remote is no power for a good half mile or more and no communications other than cellular service for further than that. The guy who will be checking lives about 5 miles away. The Control device will be sitting above ground in a protected case similar to a plastic toolbox.

Kyle, I like the idea of the multiplexer, it only has 16 channels but with only 4 ports to use I can easily use 2 of them to read all 21 sensors and sparkfun already has them on breakout boards. You item link got me thinking and I found an item from digikey that has 32 channels so I don't need to try to read from 2 different multiplexers. Thanks!

Gdeaver, I found a tutorial about using the maxim DS18B20 connected to an aruindo and a program to read the value so if I use it I am already partway there in programming too! Thanks!