From The New-York Times January 3, 1862:
IMPORTANT FROM WASHINGTON; … ARMY TELEGRAPHS. …
… WASHINGTON, Thursday, Jan. 2. …
The Army Telegraph Corps have returned from Hancock, having completed telegraphic connection between Frederick and Wheeling. They will next proceed to Budd’s Ferry, and extend the telegraph line from thence to Point Lookout. A cable will be run from there to Fortress Monroe. …
The U.S. Military Telegraph Corps included operators and the Telegraph Construction Corps, which “built a total of 15, 389 miles of field, land, and submarine telegraph lines” during the Civil War. According to Google Maps about 225 miles would have been run between Frederick, Maryland and Wheeling in western Virginia. The Construction Corps even built lines during the course of a battle. The U.S. Military Telegraph Corps was mostly a civilian organization. Both the CSA and the USA developed military signal corps during the war. There is a section on the two Civil War Signal Corps (as well as some information on the civilian Telegraph Corps) in Getting the Message Through by Rebecca Robbins Raines.