The prefix 'intra' stands for 'into' or 'inside'
As in 'intranet' or 'intravenous'.
So 'intracounty move' should mean a move towards the inner part of a county.
This could be from a political point-of-view, like a political campaign aimed for the inner county's population. Or maybe a military one: Like during a war, a comander sends the army towards the inner part of the county, for strategic reasons.
And 'inter' means 'between'.
As in 'interaction' - action between two or more people (or other living beings).
This should mean a move between counties! (From the same perspectives as explained above).