The Army of Relief grew to about 30,000 effectives in
late June. It had 4 infantry and 1 cavalry division.
When Johnston arrived at Jackson (ca. 16th May) it was defended by Gregg's brigade up from Port Hudson (2,745 PFD by last return) and had taken an utter pounding, pulling out of the town. Another brigade from Port Hudson was with Loring (Buford's, 2,735 and not counted in the last return of Loring's division).
Two more brigades reach the vicinity of Jackson around the day of the Battle of Jackson (14th May) - Gist (2,456) and Walker (2,379) have been sent from the SC coastal defences. This gave Johnston 7,580 (minus losses) to defend Jackson.
After Grant turns west more reinforcements arrive.
Two brigades from Bragg's army have been dispatched. Ector (1,154) is the first arriving on 21st, and Loring's Division (minus Waul's Texans) have also just arrived. On this day Johnston formally forms the 4 loose brigades (Gregg, Walker, Gist and Ector) into a division under Walker, giving him two divisions. The second brigade, McNair's (1,432) arrives around 26th.
Maxey (2,747) was already en route towards Jackson from Port Hudson and was 60 road miles from Jackson when news reached him that Gregg was hard pressed. He aborted and marched further east, linking up with Johnston around 31st May. A third brigade from SC, Evans' (2,051) arrives on the 30th or 31st. The three late arriving brigades (McNair, Maxey and Evans) are formed into a division under MG French.
Breckinridge's Division (brigades of Adams, Helm and Stovall, 6,143) from Bragg's army arrives ca. 1st June, giving Johnston 4 infantry divisions. At a similar time (perhaps a day or two later) Jackson's cavalry division (brigades of Cosby and Whitfield) also arrived.