Found a little more info , I think

You can check this out on
www.freecen.org.uk1841 Census
Address- Camelon, Falkirk, Stirlingshire
Jas. Montgomery M Age 70 Merchant Born outside Census County
Agnes Montgomery F Age 65 ditto
John Montgomery M Age 20 ditto
There are also 6 men staying at this address (probably lodgers and they all have the occupation of Mason)
1851 Census
Address - Camelon, Falkirk
Agness Montgomery Head Widow age 70 Cow Feeder born Midlothian, Mid Calder
Jane Montgomery Granddau age 7 Scholar born Falkirk, Stirlingshire
Also 2 House servants.
also at Camelon
Robert Montgomery Head age 41 Labourer at Naphta Works born West Lothian, Linlithgow
Jean Montgomery wife age 42 Publican born Falkirk, Stirlingshire
Agnes Montgomery dau age 19 House Servant ditto
James Montgomery son age 17 Tracker Canal ditto
John Montgomery son age 15 Cowfeeder's servant ditto
Robert Montgomery son age 13 Scholar "
Cecilia Montgomery dau age 11 scholar "
Malcolm Montgomery son age 9 scholar "
Willm Montgomery son age 5 scholar "
Phew!! I think the above 1841 entry is James Montgomery and Agnew Davidson. The couple also seem to have had a son John Montgomery born at Whitburn
https://familysearch.org/pal:/MM9.1.1/XYW9-23JHe would have been 23 at the time of the 1841 Census but ages on this Census can be unreliable as adults were instructed to round their ages down to the nearest 0 or 5.
The 1851 Census, I think is Agnes Davidson/Montgomery as a widow. Robert is, I think, her son born in 1808.
Looby
