Deyra Doon, Or Dehra Doon, a valley of British India, between the S. W. base of the lowest and outermost ridge of the Himalaya and the N. E. slope of the Sivalik mountains, the former having an elevation of 7,000 or 8,000 ft., and the latter of about 3,000; between lat. 30° and 30° 32' N., and Ion. 77° 43' and 78° 24' E. It is bounded S. E. by the Ganges and N. by the Jumna, is drained by their tributaries, and with the hilly region called Jounsar Bawur forms a district under the lieutenant-governorship of the Northwest Provinces. The productions are rice, maize, grain, cotton, sugar, opium, indigo, plantain, and hemp. Every English plant is said to thrive luxuriantly, and considerable success has attended the cultivation of tea. The valley is watered by numerous streams, and abounds in game. The climate during part of the year is very unhealthy. The district was formerly included in the dominions of the rajah of Gurh-wal, was overrun by the Gorkhas in 1803, and in 1815, during the Nepaul war, was invaded by the British, who suffered great loss here, and who, after the expulsion of the Gorkhas, kept possession of the territory. - Deyra, the principal town of the district, is situated in dense mango groves, at the intersection of two routes of trade, 2,369 ft. above the sea, and 125 m.

N. N. E. of Delhi.