The 1841 census for Farnley is covered by film HO107/1343, Enumeration Districts 17 to 19.
The File is split here by Enumeration District. Farnley had 292 households totalling 1,530 people at the time of the census.

The 1841 census is the oldest surviving census for Farnley, taken on the 7th June 1841. The returns for 1841 were the first that were archived completely. The census itself simply listed the names of each person in the household, gave the occupation of the head and the age, rounded down to the nearest five years for all those older than 15. Sometimes the census enumerators forgot or ignored their instructions and put the correct ages and occupations of other household members. This was the case in the districts in Farnley.

Farnley was still an agricultural area with a few mills and coal mines in 1841. The great Ironworks and Brickworks which were to completely dominate the area for a century were still unopened.
The area seems to have been going through a lean period if the notes made by enumerator Jeremiah Pickersgill are anything to go by. At the end of the returns for ED17, he notes that 145 manufacturing labourers (71 female, 74 male) had left the district for want of work. Whether he means in the area of his own district or across the three enumeration districts isn't clear.