Tergnier (French pronunciation: [tɛʁɲe]) is a commune in the department of Aisne, Hauts-de-France, France. Its location on the Canal de Saint-Quentin and the Creil–Jeumont railway (Tergnier station) supported its development as an industrial centre in the second half of the 19th century.

The commune of Tergnier absorbed the former communes of Fargniers and Vouël in 1974, and Quessy in 1992. Since the 2020 municipal elections, Michel Carreau has been the mayor of Tergnier.

Tergnier is twinned with the municipality of Wolfhagen (Germany) since 17 May 1981.

The population data in the table and graph below refer to the commune of Tergnier proper, in its geography at the given years, i.e. excluding former communes that were absorbed at a later date.

Historical population

Year Pop. ±% p.a. 1793 222 —     1800 249 +1.65% 1806 263 +0.92% 1821 223 −1.09% 1831 269 +1.89% 1836 258 −0.83% 1841 276 +1.36% 1846 273 −0.22% 1851 304 +2.17% 1856 862 +23.18% 1861 1,235 +7.46% 1866 1,806 +7.90% 1872 2,572 +6.07% 1876 3,079 +4.60% 1881 3,536 +2.81% 1886 3,708 +0.95% 1891 3,740 +0.17% 1896 3,960 +1.15%	Year Pop. ±% p.a. 1901 4,084 +0.62% 1906 4,307 +1.07% 1911 4,898 +2.61% 1921 2,076 −8.23% 1926 3,453 +10.71% 1931 4,080 +3.39% 1936 4,357 +1.32% 1946 3,370 −2.54% 1954 5,002 +5.06% 1962 5,827 +1.93% 1968 5,949 +0.35% 1975 11,736 +10.19% 1982 12,032 +0.36% 1990 11,698 −0.35% 1999 15,069 +2.85% 2007 14,722 −0.29% 2012 14,110 −0.85% 2017 13,456 −0.94%
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Source: EHESS and INSEE (1968-2017)

• Communes of the Aisne department