Loch Brown or Loch Broon as it was known as in the previous centuries, was situated roughly between the farm of Skeoch, and Crosshands.
It was referred to in the first statistical account (1791 - 1799) of Mauchline Parish by Rev Auld (Burns' Daddy Auld) as follows:

"The only loch in the parish, called Loch Brown is about three miles North West from Mauchline.
Wild ducks, geese. and sometimes swans resort to it.
It covers about 60 acres of ground and would have been drained many years ago,
had it not been for the sake of two corn mills which it supplies with water"

The site of Loch Brown as seen today. Click for a higher res image.

Article on Loch Brown from Kilmarnock Standard in 1933 about the draining of the Loch in the 1840s to make way for the railway.

Armstrong's map from 1775 with Loch Broon at the top left .