The National Library of Scotland has a digital image of the 1817 chapbook printed by J.Fraser of Stirling which contains the earliest dated text of 'The Isle of St. Helena'; it can be viewed via this link Isle of St Helena, Chapbook 1817. It is an eight page booklet containing The Isle of St helena, Banks of Doon, Highland Harry, Ralph and Moses, and Dull Care. There is a handwritten note on the last page "William Henderson his Ballads 1819".

I'll post the full text below for comparison with other versions.

Isle of St Helena (Roud 349)

Now Boney is awa,
From his warring and fighting,
He is gone to a place,
That he ne'er can delight in.
He may sit now and tell
Of the scenes he has seen a',
While forlorn he doth mourn
On the isle of St Helena.

No more at St Clouds
He'll appear in great splendor,
Nor go forth with his crouds,
Like the great Alexander.
He may sigh to the winds,
By the great mount Diana,
With his eyes o'er the waves,
That surrounds St Helena.

Now Louisiana weeps
For her husband departed,
She dreams while she sleeps,
And awakes broken hearted.
Not a friend to condole,
Even those that might they winna,
And she mourns while she thinks
On the isle of St Helena.

The rude rushing waves
A' our shores round us washing,
And the great billows heaves,
A' the wild rocks a dashing.
He may look upon the moon,
And think on Louisiana,
With his heart full of woe,
On the isle of St Helena.

Now ye that have great wealth,
Beware of ambition;
For some decree of fate
May change your condition,
Be ye stedfast in time,
For what's to come ye kenna,
[May] be your race may end
At the isle of St Helena.

No tune is given in the chapbook, nor is any author credited.