Western sources place the origin of the Croad Langshan at the Guangjiao Temple, Langshan Hills, China.
Major F.T. Croad received the first birds in 1872 and his niece, Miss A.C. Croad, subsequently developped the breed.
America imported Langshans from China and England, not much later .
Australia independently imported Langshans from China and created the Australian Langshan.
According to Miss A.C. Croad  the first imports received from China in 1872 came from the Langshan Crossing on the northern bank of the great Yangtze River, about 100km from Shanghai and close to Nantong (see map)
In her book  she writes:
A letter bearing date November 27th 1871 conveyed to the late Major Croad intelligence that a nephew residing in the north of China, had made the purchase of a new breed of fowls for him. Successive letters made mention of these birds.
“The fowls I am sending you are very fine; their plumage is of a bright, glossy black. I am told that their flesh is excellent. The Chinese say they are allied to the Wild Turkey. They are valuable birds — you must be careful of them, and get them acclimatised by degrees.”
Extracts from THE LANGSHAN’S AMAZING HISTORY – Fowls of the Wolf Mountain that have always been here – By Martyn Pierre Gurney. 
“In the north bank of the great Yang-Tse River, about sixty miles from the Yellow Sea and a hundred miles from Shanghai, rises the solitary “wolf mountain”, Lang-Shan. Entirely wooded, crescent-shaped, it runs in a north-easterly direction, facing to the north-west, the small town of Tung-Chow * , buried almost among the rice fields and canals. The mountain has three tops, not two as hitherto supposed. Two at the points of the crescent and one in the centre, the latter protruding somewhat westward, crowned with its beautiful fourteenth century pagoda.”
* Tung-Chow: today Nantong
The area was densely populated, but difficult to access:
“M. Soulié de Morant  assures me that the European merchants and residents at Shanghai going up the river to Nan-Kin had no occasion to land and never to his knowledge did land on the north bank of the river near the Lang-Shan mountain. Between Shanghai and Kiang-Yin** the Yang-Tse Kiang is very broad. At the Langshan flats it is nearly ten miles wide, and the many sandbanks, covered at high tide or when the river is in flood, render navigation extremely difficult. The only navigable channel for steamers never gets near the north bank until the small riverside village of Chuang-Yan*** is reached.”
** Kinag-Yin = Jiangyin 江阴
*** Chuang-Yan = Chouang-Yang = Changjiangzhen 长江镇
Traffic within the area was restricted to foot and boat traffic.
“From Chuang-Yan to Tung-Chow, the only town within sight of the mountains there is no road, only a canal, and tow paths run along its banks. No road of any kind exists in the district. There are pathways only, along the canals and between the rice fields, just broad enough for one man to run along, pushing a narrow plank, fastened to one wheel and having a pair of handles at one end and a small mast at the other, up which a square sail is hoisted when the wind is favourable. This is the only conveyance at the disposal of the European traveller or the well to do native.”
“M. Soulié de Morant tells me he was greatly surprised to find all the inner courtyards of the lower Monastery buildings where the apprentice monks and the servants of the Monastery lived, and in all the farms lying around the mountain and belonging to the Monastery, “beautiful, large, full bodied black fowls with a green metallic sheen”, and these only.”
Miss Croad  writes:
“The priests at the Temple look upon them as “Joss,” or sacred birds. At one time we know they made great difficulty in parting with any specimen. When they are in full moult is the outer “barbarians” best time, for they are then considered unfit to offer to their gods.”
-  A.C. Croad: The Langshan fowl; its history and characteristics with some comments on its early opponents (3rd edition), Bowers Brothers, London 1889.
-  THE LANGSHAN'S AMAZING HISTORY - Fowls of the Wolf Mountain that have always been here - By Martyn Pierre Gurney. (year unknown; around 1930?) (get the full text in pdf here)
-  Wikipedia: M. Soulié de Morant had the opportunity to start learning Chinese at the age of eight, being taught the language by a Jesuit priest. Although he had originally intended to become a physician, he had to give up his plans when he father died. At the age of twenty, Soulié de Morant was employed by a bank, which decided to send him to China in 1899. Given Soulié de Morant's command of the Chinese language, he soon joined the French diplomatic corps, for which he would work for most of the following two decades. He served as French consul in Shanghai and Kunming and French Mixed Court in Shanghai.