NPA-NXX - 605-666

This is the 605-666 subcode (NPA-NXX) prefix page. Follow a prefix to find the number you are looking for. We divide our pages up to make them more user friendly to navigate!

1. Area Codes
2. 605
3. 605-666

The 605-666 subcode mainly covers Keystone in Pennington county. But other numbers maybe included as well.

We have a database of information derived from the public phone records of South Dakota state. Many of the numbers in this subcode are Regular Landline registered to Mt Rushmore Telephone Company. We hear they employ a large number of people in the South Dakota office.
Recently there have been an increase in reported calls, we've had over 100948 comments across our systems for the 605-666 subcode.