A Corn Mill on this site (at Shean, Liggartown) was mentioned in the Civil Survey of 1640 as part of the Abercorn estate. Galbraith Hamilton became the tenant in about 1729 and, on the adjoining lands, established a Bleach Green which was abandoned around 1779.

In the 1750s, the Mill was in need of rebuilding, and Hamilton was advised to add to it a Wheat mill, for which he was loaned £100 by the Marquis of Abercorn. He also petitioned the Irish House of Commons in 1765 for financial assistance in building the Mill. However, this venture did not prove successful. In the 1780s, Abercorn intervened personally and more than £1,000 was laid out on improving the Seein mill. This included £39 for two French millstones and £36 for a stove for drying wheat. Abercorn brought in Alexander Stewart to design and build it. Stewart later became Clerk of Works during the building of Castle Coole.

In 1828, this mill was rebuilt by Abercorn, but shortly afterwards became incorporated in the flax spinning mill standing here today, having been purchased by way of a 500 year lease by the Herdman brothers, James, John and George, in 1835 in partnership with the Mulhollands (Andrew and Sinclair) and Robert Lyons. By 1849, the Herdmans were the sole owners, having bought out their partners. A map of 1846 shows the "Old Mill" as measuring 248 ft long by 48 ft wide. In 1879 a third storey was added. This Mill became known as the Tow Mill and was where the hackling of the flax took place.

HISTORY OF POWER

1839 2 Water wheels producing 70 horsepower.

1840 Weir completed (paved in 1858 with roman cement and square stones).
Watercourse built - 35 ft wide, 6 ft deep.

1842 Gasworks (coal-fired) erected.

1843 All houses in village provided with a gas light, the shop with 4 lights and lamps on the road.

1845 New waterwheel installed.

1849 4 Waterwheels producing 600 horse power and Steam Engine.

1865 New "walking beam" engine installed (the last word in its day). Named "Gladiateur" after that year's winner of the Derby. It continued working for 41 years.

1870 New Sluices built.

1892 Electric light in Mill. 250 lights from its own dynamo.

1900 - 03 Turbines installed. 1000 horsepower.

( To calculate waterpower : 720 cubic ft falling one foot per minute is equal to one horse power. Take depth and width of watercourse. Multiply by number of feet passing per minute and multiply the result by the fall, then divide by 720).
Width of watercourse/35 ft x Depth/6 ft x Speed full water per minute/242 ft = 51000 ft x by fall of 14 ft per minute, divided by 720 gives practically 1000 horsepower).

1919 - 20 DC Turbines installed in new small Turbine House providing 135 horsepower to produce lighting for the Mill, the village, Sion House and Camus House.

1989 Turbines abandoned when all operations moved to new Mourne Mill.

1995 New turbines installed with potential to produce 850 kw. This power sold to the grid which provides an income to help subsidise Herdmans' flax-spinning business.

HISTORY OF MAIN MILL

The Main Mill was built in 1853 to 1855. The Architect was William Lynn of Lanyon Lynn and Lanyon, Belfast. Built of grey ashlar stone quarried locally in Douglas Bridge. The builder was John McCracken. The building was designed as a fireproof mill. This building was used for preparing and spinning until 1989 when the Mourne Mill was opened and it was abandoned.

The Line Preparing frontage and Mechanics Shop were built in 1888 with yellow brick from Kilmarnock.

A two storey yellow-brick extension was built in 1888 by J. Ballantine and Co. Derry, designed by William Lynn (known as the New End).

Three storeys were added to the New End in 1907 with no pillars thus leaving more room for longer machines. This was achieved by buttressing the walls and using girders of very heavy section.

The main Mill was built wider than normal for spinning mills, which enabled Herdmans to survive in later years when others couldn't, because they were able to accommodate larger machines.