Various bits of info from the Maryland Manual, 1967-68 (Volume 173 in the Maryland state archives -
http://aomol.net/html/index.html )
1964 Presidential primary results between the Johnson stand-in (Daniel Brewster) and George Wallace
Allegany: 78/19 Brewster
Anne Arundel: 63/35 Wallace
Baltimore City: 59/35 Brewster
Baltimore County: 48.3/48 Brewster
Calvert: 66/32 Wallace
Caroline: 68/29 Wallace
Carroll: 50/46 Wallace
Cecil: 57/39 Wallace
Charles: 68/30 Wallace
Dorchester: 80/18 Wallace
Frederick: 60/37 Brewster
Garrett: 76/18 Brewster
Harford: 48/47 Wallace
Howard: 51/46 Wallace
Kent: 67/31 Wallace
Montgomery: 70/26 Brewster
Prince George's: 51/47 Brewster
Queen Anne's: 62/35 Wallace
Somerset: 73/25 Wallace
St. Mary's: 63/34 Wallace
Talbot: 63/34 Wallace
Washington: 66/30 Brewster
Wicomico: 71/26 Wallace
Worcester: 80/17 Wallace
total: Brewster 53, Wallace 43
Also, Mahoney won the 1966 gubernatorial primary with 30% (winning by a 1939 vote margin).
Mahoney won majorities in Calvert, Charles, and St. Mary's in the primary.