The 1831 census for Aghagaskin records 1 James Lenox. He had 3 males and 6 females in his household. All were Church of Ireland. There were numerous other Lenox households in the townland who, typically, would be relations (David, Henry, Bachus, John & Margaret).
http://www.census.nationalarchives.ie
There are 6 Len(n)ox probate abstracts on the PRONI website for the families in Aghagaskin, starting with this:
Letters of Administration (with the Will annexed) of the personal estate of William Lenox otherwise Lennox late of Aghagaskin County Londonderry Farmer who died 28 July 1876 at same place were granted at Londonderry to James Lenox otherwise Lennox of Aghagaskin the Son and a Legatee.
The above will is on-line on the PRONI site. For the others you need to contact or go to PRONI to get the paper copies. (William’s death cert indicates he was 70, so born c 1806).
http://apps.proni.gov.uk/DCAL_PRONI_WillsCalendar_IE/WillsSearchResults.aspx
5 Lennox families in Aghagaskin in 1901:
http://www.census.nationalarchives.ie/pages/1901/Londonderry/Magherafelt/Aughagaskin/
You can use Griffiths Valuation and the subsequent revaluation records to trace the families forward from the 1860s.
http://www.askaboutireland.ie/griffith-valuation/index.xml
http://www.proni.gov.uk/index/search_the_archives/val12b.htm
PRONI has this document that may interest you (ref D3000/106/1):
Genealogical file relating to members of the Garrett, Lennox and Foster families from the area around Magherafelt, Co. Londonderry (townlands of Aghagaskin, Ballyheifer and Leckagh, parish of Magherafelt, and Aughrim, parish of Artrea), and various places in Australia, Canada and the United States (c.1732-1984).
The normal situation in Ireland which (as I think you may have already found from your personal experience) is that most families only know their own history back about 3 generations back to around 1900 in todays terms. For earlier research, you might need to employ a researcher to piece the records together.
Maghera local site:
http://www.magheragenealogy.org
They have a lot of local gravestone records.
The Len(n)ox families originated in Scotland in the 1600s but I expect you know all that. The Lennox (and later Lennox-Conyngham) family lived at Springhill House, nearby at Moneymore. The original settlers brought tenants with them from their Scottish estates. Presumably your ancestors were amongst them. See:
http://www.nationaltrust.org.uk/springhill
Griffiths Valuation lists 2 James Lennox in Aghagaskin in 1859. One had land on plots 29 &30 totaling around 12 acres. The other, with the agnomen (nickname) “tight” had plot 31, which was a 6 acre farm. I have no idea why he was known as “tight”. I couldn’t begin to imagine. But that’s how he is recorded in Griffiths. Perhaps local knowledge may answer that question for you. Both of those properties are easy enough to locate today. They are all on either side of Bowman’s Rd, near the Castledawson Roundabout, but you will need a Griffiths map to locate them precisely.
http://www.askaboutireland.ie/griffith-valuation/index.xml