In this article by Asim Awan, the writer mentions the Hindu and Sikh population of Sargodha (map) in 1947 prior to Partition.

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I told Khushwant Singh about the large Gurdwara in Sargodha that is now called the Ambala Muslim High School. Sargodha was the district headquarters of the district Shahpur of which Khushab was a tehsil. In 1947 the population of Sargodha city was 36,000 with only 6,000 Muslims and a very large Sikh presence. All Hindus and Sikhs went to India as post-Partition violence erupted and the city was taken over by Muslim refugees from the east Punjab city of Ambala. The large Sikh Gurdwara located in the city centre was converted to a school for boys. There was an exceedingly deep and sad look on his face as he thought of the horrors he had witnessed.