Julius Nicolai Jacobsen (19 May 1829 – 25 December 1894) was a Norwegian businessperson and politician. Based in Græsvig, a settlement built around his sawmill Græsvig Brug, he founded the company J. N. Jacobsen & Co. which was successful during his lifetime.
He was born in Strømsø as the son of a sexton. He moved to Fredrikstad (then Fredriksstad) in 1848, working for merchant Peter Gellertsen. He then became a self-made businessman, settling at the property Lykkeberg which he bought in 1855. Having amassed a large property at Græsvig in Onsøe outside of Fredrikstad through transactions in 1856 and 1859, he founded a sawmill Græsvig Brug on 1 January 1860, the same day as national sawmill privileges limiting private enterprise were abolished. The sawmill was a catalyst of growth, spurring a significant immigration to the district. For the children of workers at the sawmill, a school was founded in 1862. Later followed a gospel hall in 1866 and a chapel in 1884. The company was renamed J. N. Jacobsen & Co. in 1863, his brother entering as a business partner.
Jacobsen served as a deputy representative to the Norwegian Parliament during the term 1877–1879, representing the constituency of Fredriksstad. He was also a member of the city council's executive committee from 1868 to 1894, and served as deputy mayor for some time.
In 1858 he married Olivia Bredesen, born in 1841 in Sør-Odal. Jacobsen subsequently ordered the erection of a new house at Lykkeberg, drawn in Gothic style by the nationally known architect Paul Due. The house was finished in 1875. However, Olivia died in 1879 after giving birth to their eighth child. A local urban legend has it that she haunts the house.
Jacobsen was proclaimed Knight of the Royal Norwegian Order of St. Olav in 1882 and Commander of the same order in 1894. The city council named a street in Fredrikstad after him in 1894, while he was still alive. Following his death later that year, J. N. Jacobsen & Co. was transformed to a limited company. His brother took over the leadership, together with Julius' son-in-law J. C. Juel. The youngest son Andreas Julius Jacobsen was involved from 1907.