Tongliao is a prefecture-level city in eastern Inner Mongolia, People's Republic of China. The area is 59,535 square kilometres (22,987 sq mi) and as of the 2020 census, its population was 2,873,168 (3,139,153 in 2010). However, the city proper made of Horqin district, had 921,808 inhabitants. The city was the administrative centre of the defunct Jirem League.

The original Mongolian name for Tongliao city proper (i.e. Horqin District) is Bayitalai (Chinese: 白音泰赉/巴林太来; pinyin: Báiyīntàilài; lit. 'having buildings'), while the original name of the prefecture-level city is Jirem. The Mongolian dialect spoken in this area is Khorchin Mongolian.

Human settlement in Tongliao and the surrounding Khorchin area dates from at least 1000 BC. The Donghu people, a tribe who spoke a proto-Mongolian language, settled in today's Tongliao area, north of Yan during the Warring States period. their culture was associated with the Upper Xiajiadian culture, characterized by the practice of agriculture and animal husbandry supplemented by handicrafts and bronze art. Later, the Tongliao area was controlled by Xiongnu, Xianbei, and Khitan tribes.

After the Mongolian Khanate ovcupird the area, Tongliao was put under the jurisdiction of Liaoyang province, whose provincial capital was in today's Liaoning Province. In the early 1617, Khorchin, Dörbod, Jalaid and Gorlos tribes met in Jirem to establish an alliance, and the Jirem League was founded in 1636 to administer Khorchin territory. The Jirem League had jurisdiction over six Khorchin banners, two Gorlos banners, one Dorbod banner and one Jalaid banner. During the Republican period, the Jirem League and the surrounding Khorchin area was controlled by the Fengtian and Liaoning provinces.

In 1918, Tongliao County was first established under the administration of the Jirem League and Fengtian province. After the Japanese invaded northern China in 1931, the Japanese attacked Tongliao urban area and soon divided it into four parts, in order to govern the western part of former Heilongjiang, Jilin and Fengtian provinces. These Xing'an provinces roughly overlap today's eastern part of Inner Mongolia, including today's Hulunbuir League, Xingan League, Chifeng and Tongliao. After the dissolution of the Manchukuo state, the Jirem League was governed by Liaoning and Liaobei provinces until Ulanhu established Inner Mongolia in Ulanhot, governing eastern Mongolian areas including the Hulunbuir, Jirem and Ju Ud leagues. After 1969, the Jirem League was put under the administration of Jilin province administration for 10 years until 1979. In 1999, the Jirem League became defunct and changed its name to Tongliao city, which was set up a prefecture-level city.

In 1924, Oomoto leader Onisaburo Deguchi, Aikido founder Morihei Ueshiba, and Lu Zhankui were arrested by Chinese authorities in Tongliao. Lu and his men were executed by firing squad, but Deguchi and Ueshiba were released into the customer of the Japanese consul.

Tongliao spans latitude 42°15' – 45°41' and longitude 119°15' – 123°43', and borders Jilin province to the east, Liaoning to the south, Chifeng to the southwest, the Xilin Gol League to the west, and the Hinggan League to the north. Not far from Tongliao are silica sands. Tongliao has a total area of 59,535 square kilometres (22,987 sq mi), accounting for 5.4% of Inner Mongolia's total.

Tongliao's topography primarily consists of plains, though the northern stretch of the prefecture extends into the eastern foothills of the southern Greater Khingan. The central and eastern parts of the prefecture are marked by the plains of the Xiliao, Xinkai River (新开河), and Jiaolai rivers (教来河), collectively forming the Sanhe Plain (三河平原; 'three rivers' plain'). The highest point in the prefecture is Tunte'er Peak (吞特尔峰), at 1,444.2 m (4,738 ft).