A second area Sonic drive-in is opening at 2564 Ironwood Drive in Sun Prairie, near the corner of Windsor Street and Grand Avenue, by the Copp's grocery.
City planner Tim Semmann said the restaurant is expected to open in September.
The first Sonic in the area opened on University Avenue in Middleton in 2009. The Oklahoma-based Sonic chain has about 3,500 locations throughout the U.S.
Construction has also started on the city's third McDonald's, immediately north of Woodman's grocery store in Sun Prairie. The address is 939 Bunny Trail, although the façade is on Prairie Lakes Drive.
Semmann said he anticipates it opening in October.