Weeks and Day was an American architectural firm founded in 1916 by architect Charles Peter Weeks (1870–1928) and engineer William Peyton Day (1886–1966).

Weeks was born in Copley, Ohio, educated in the atelier of Victor Laloux at the École des Beaux-Arts from 1892 to 1895, and briefly partnered with John Galen Howard. (Weeks is unrelated to the Canadian-American architect W. H. Weeks, also practicing in San Francisco in these years, and is also unrelated to William E. Weeks, architect in Southern California.^[1])

Day had been in partnership with pioneering San Francisco reinforced concrete engineer John B. Leonard. With Weeks as designer and Day as engineer, the firm specialized in theaters and cinemas, including several exuberant movie palaces and hotels in the San Francisco Bay Area, extending to Los Angeles and San Diego.

The firm was most active immediately before Weeks' death in 1928. Day continued the firm for 25 more years, closing the firm in 1953.

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Architectural work

• Loew's State Theatre, downtown Los Angeles, 1921
• Don Lee Cadillac Building, San Francisco, with architectural sculpture by Jo Mora, 1921
• California State Office Building (now Jesse M. Unruh State Office Building) and the Library and Courts Building, and fountain court inbetween (1922-1928), which make up the NRHP-listed Capitol Extension District,^[1] 900 block of the Capitol Mall, Sacramento, California (Weeks & Day)
• Huntington Apartments, 1922, converted to Huntington Hotel in 1924, Nob Hill, San Francisco
• headquarters of the San Francisco Chronicle, 901 Mission Street, San Francisco, 1924
• Stanford Theatre, Palo Alto, California, 1925
• Mark Hopkins Hotel, San Francisco, 1925
• Brocklebank Apartments, Nob Hill, San Francisco, 1926
• Hotel Sainte Claire, San Jose, California, 1926
• Peninsula Theatre, Burlingame, California, 1926
• Schlage Lock "Old Office" and Plant 1, San Francisco, 1926
• California Theatre, San Jose, California, 1927
• Fox Oakland Theatre, Oakland, California, 1928
• Fox Theater, now Copley Symphony Hall, San Diego, California, 1928
• Sir Francis Drake Hotel, San Francisco, 1928
• Cathedral Apartments, Nob Hill, San Francisco, 1930
• I. Magnin Building, Oakland, California, 1931
• Fox-Oakland Theater, 1807–1829 Telegraph Ave., Oakland, California (Weeks & Day), NRHP-listed^[3]
• Hotel Sainte Claire, 302 and 320 S. Market St., San Jose, California (Weeks & Day), NRHP-listed^[3]
• Don Lee Building, 1000 Van Ness Ave., San Francisco (Weeks and Day), NRHP-listed^[3]
• Baker and Hamilton, 601 Townsend St., San Francisco (Weeks, Charles Peter), NRHP-listed^[3]
• Administration Building, Treasure Island, built 1938, SE Corner of Avenue of the Palms and California Ave., Treasure Island, California (Day, William Peyton; Kelham, George William), NRHP-listed^[3]
• Hall of Transportation, Treasure Island, SE Side of California Ave. between Aves. D & F, Treasure Island, California (Day, William Peyton, Kelham, George William), NRHP-listed^[3]
• Palace of Fine and Decorative Arts, Treasure Island, SE Side of California Ave. between Avenue F and Avenue I, Treasure Island, California (Day, William Peyton; Kelham, George William), NRHP-listed^[3]