The success of the Boston Manufacturing Company Mills led to the development of a new center of commercial and public activity along the adjacent Main Street corridor and its intersection with Moody Street across the Charles River. In 1827, the Boston Manufacturing Company built Rumford Hall on adjacent land, now the town common. After 1849, Rumford Hall served as the town hall until 1924, when the current City Hall, a five-part limestone Classical Revival design (NRD) by Kilham, Hopkins and Greeley, replaced it. Commercial structures quickly came to line the town common, one of the earliest survivors being the red brick Italianate Central Block (617–627 Main Street, NRD), designed by local architect Henry W. Hartwell. Farther west facing the town common, George F. Meacham designed the polychromatic Whitford Block (633 Main Street, NRD) in 1877. (Meacham, best known for the Boston Public Garden [
BB1], also designed the Civil War monument on the Common.) Nearby, the Music Hall (15 Elm Street, NRD) rose in 1880 to the designs of Henry Hartwell. In 1885, Waltham celebrated its establishment as a city with ceremonies on its second-floor stage.

Beyond the town common commercial core, major institutions chose Main Street as it extended to the west. Churches marked the importance of the mill economy when the Trinitarian Congregationalists separated from the Unitarian Church of Christ and constructed a new church (730 Main Street, NR) in 1870, a clap-boarded structure (now encased in aluminum siding) with staged tower and steeple that retained the image of a colonial meetinghouse. The expanding Episcopal parish built the dramatic Christ Church (750 Main Street, NR) in 1898, using field-stones from the Waltham estate of philanthropist Robert Treat Paine to carry out the nubby design by Peabody and Stearns. Across Main Street, Loring and Leland provided a handsome design in Federal Revival brick for the Waltham Public Library (1915, 1994 expanded, Shepley, Bulfinch, Richardson and Abbott, 735 Main Street, NR). In 1935–1936, Boston architects Wadsworth, Hubbard and Smith designed the U.S. Post Office (774 Main Street, NR), a two-story brick Colonial Revival building and a typical product of the Public Works Administration.