1911 - Millinocket's population reaches 5,000.
1913 - A milk inspector is appointed and the Fire Department receives a Knox combination chemical and hose motor truck.
1914 - Aroostook Avenue School is built.
1919 - November 11, Millinocket Memorial Library is dedicated and the Cooperative Store is built.
1920 - Dr. C.S. Bryant opens Millinocket's first surgical hospital, Millinocket Light Co. installs electric lighting, the Fire Dept. receives a LaFrance pump, hose and chemical truck, and the town's first playground opens on July 6.
The early 20's also see Maine and Highland Avenues extended to Bowdoin Street with more houses built on the Flat. A concrete road, the first of its kind, is built on Katahdin Avenue and Central Street. The Millinocket Water Company installs a chlorinator for sterilizing drinking water.
1921 - The Millinocket High School burns down on November 13.
1923 - In September, Stearns High School opens.
1925 - The Millinocket Chamber of Commerce is formed and the Fire Dept. acquires a Ford truck for still alarms and grass fires. Millinocke also saw some Ku Klux Klan activity in 1925.
1926 - Millinocket celebrates its 25th Anniversary. Stearns High School gymnasium is built and a public bathing beach opened in the Pines.
1927 - The Central Street bridge is rebuilt and Bangor Hydro-Electric buys Millinocket Light Company. Streets were named, houses numbered, and mail delivery began. The year also saw the first storm sewer built and a plumbing code was established.
1928 - Bangor Hydro-Electric Company installs new street lights, the Bandstand is placed in the park, and a municipal skating rink was opened. On January 3, GNP Co. President, Garret Schenck dies.
1929 - Electricity is installed in Little Italy. The school system establishes a health program and hires a school nurse.