The unions were a part of the Millinocket workplace from the beginning. The first people recruited to work at the new mill were mostly union men. The International Machine Tenders Union was representing GNP workers as early as 1901, and the first local union was formed the following year, #27 of the International Brotherhood of Paper Makers.
Other unions were formed shortly afterward, including Local Union #69 of the International Brotherhood of Firemen, Oilers, and Helpers; and in 1906, Local Union #12 of the International Brotherhood of Pulp, Sulphite, and Papermill Workers.
The 1920s brought rapid growth in Millinocket. The addition of two more paper machines greatly increased the workforce, which in turn increased the population of the town.
The town was growing to the west so fast that the Elm Street railroad crossing could no longer meet the demands, so another was built at Spruce Street, extending the town further. Maine and Highland Avenues were extended to Bowdoin Street.
The Millinocket Oddfellows built a two-story brick building, which included a basement, and housed a lodge room, assembly room, dining and kitchen facilities.
A new, wider bridge replaced the original Central Street bridge over Millinocket Stream, as many Millinocket residents were by then driving their own cars.
In the fall of 1921, the Millinocket High School burned to the ground. To complete the school year, students were crammed into the Armory building, which was partioned into four rooms, an arrangement that served the town’s high school students for the following school year, as well. The town voted to raise $30,000 by assessment, and to take out a bond for an additional $150,000. Additional money included a gift of $50,000 from the Great Northern.