In 2007, CHS had extensive renovation. The renovations included a complete overhaul of all existing science classrooms as well as the construction of a second science wing in the space formerly used for district administration offices. New ceilings and floor tiles, electrical and HVAC upgrades, and a 1,000 seat state-of-the-art Performing Arts Center (P.A.C.) were added as well. The construction, completed in 2007, gave Chelmsford High School its own auditorium for the first time in its (then) 33 year history. Previously, any performances put on by the high school were held in the 600 seat auditorium of neighboring McCarthy Middle School, formerly the town's high school. The new PAC serves as a forum for functions such as the annual Mr. CHS talent show, performances by the school's award-winning music and theater programs, and various assemblies. It is also rented out to private groups.
Further facility upgrades completed in 2008 include new enclosed stairwells at the end of the two large classroom wings to improve building flow from floor to floor, as well as a beautifully renovated library media center. New lockers have been installed in all sections of the building.
The athletic teams from CHS compete in the highly competitive Merrimack Valley Conference. Their arch rivals are their neighbors to the east, Billerica, whom they play every year in football on Thanksgiving Day, other rivals include Lowell, Dracut, Andover, and Tewksbury. CHS does have one out of conference rival, which are the Acton-Boxboro Colonials.