The Official Ontario Road Map has continually changed as the decades have passed.  The following summarizes some of the more notable changes to the layout and structure of the map.  Changes to actual road names and construction is left for those sites that focus more on the highways of Ontario.

1915
The Department of Public Highways is established on the recommendations of the Public Roads and Highways Commission of Ontario.
1923
First official map produced by the Department of Public Highways.
1926
Legend reflects that provincial highways are numbered 1 to 17.  There is no highway 1.  In 1927 the legend is altered and highway numbering begins at Highway 2. 
1929-1930
Water in coastal areas of the maps of municipalities is modernized.  Instead of multiple lines in the water, only a single line is used.
1931-1932
The Department of Public Highways is given a place in provincial cabinet with it's own minister.  The department is renamed the Ontario Department of Highways.  George Henry becomes the first minister.
Lithographed by The Copp-Clark Co., Limited
1933 - 1934
Map made of a lighter paper than in the 1931 - 1932 issue.
Fold of map changed and size changes from 37.5 W X 23.5 H to 52" W X 9.5" H
Minister name on cover changes to Leopold Macaulay.
Northern Ontario is placed on the back of the map - instead of all of Ontario being on the front side.
37 Ontario Highways shown - up from 34 on the 1931 - 1932 issue.
The "Main Highway Routes Into Ontario" Map is reduced half the 1931 - 1932 issue size.
1934 -1935
Open dimensions of map changed from 52" W X 9.5H to 45" W X 19".  The folded dimensions remain the same.
Side B of the map features a tourist orientated side with fish types according to river, railways and camp grounds.
The "Main Highway Routes" map  remains small - 5.75" X 9.25".
1935 - 1936
Premier name on cover changes to T. B. McQuesten.
"Main Highway Routes into Ontario" is quadrupled in size over the 1933 - 1934 issue.
Articles promoting Ontario as a tourist destination are included.
Five narrow route maps are included.
1936 - 1937
"Main Highway Routes into Ontario" map is produced in multi colors and called a "pictorial map".
Smith-Moir Lithographing Co., Limited, Toronto prints the map - after Copp Clark being the favored printer.
1937 - 1938
The name of the Premier of the Province appears for the first time on the cover - M. F. Hepburn.
First issue of the Official map to have Northern Ontario on the opposite side.
1938 - 1939
Lithographed by The Copp-Clark Co., Limited again
96 Provincial Highways are shown the map.
1939 - 1940
Photo - like images of people used for the first time on an Official Map Cover - the Royal couple.
King George VI and Queen Elizabeth officially open the Queen Elizabeth Way at dedication ceremonies in St. Catharines.
98 Ontario Highways shown.
First map where the small maps of communities have color added to them.
1940 - 1941
99 Ontario Highways shown on map
1941
 
1949
Premier T. L. Kennedy's name first appears on map cover for only this year.
Numbered highways are now at 105
1950
Premier Leslie Frost's name appears on the cover for the first time.
Error made in the printing of some maps - The colors red, pink, green and the blue of the water were not been applied to the back side of some maps.
1951
First year to begin using colored images routinely on the cover.
1952
Earliest sections of Highways 400 and 401 are open.
1953
Lithographing started by The Miller Litho Company Limited.
Numbered highways are now at 110
1954
Numbered highways are now at 122
1955
Map dimensions changed - closed dimensions went from 3.5" X 9.5" to 4.75" X 8.5".  Opened dimensions changed from 45.25" W X 19"  to 41" W X 25" H.  The manner in which the map was folded was also altered.
A new style of north arrow was also implemented.
James Allan's name appears as the new Minister of the Department of Highways
New lithographer - Lawson & Jones Limited, London and Toronto
Highways are numbered up to Highway 123
1956
Highways are numbered up to Highway 132
Lithographing by The Miller Litho Company Limited.
First year of the inclusion of boxed safety slogans - normally in otherwise unused areas of the map.
1957
On July 1, legislation was passed which established the Department of Transport.
Highways are numbered up to Highway 133
Lithography by Lawson & Jones, London and Toronto
1958
Highways are numbered up to Highway 135
Lithography changed to Litho Print Limited, Toronto
Original Burlington Bay Skyway opens to traffic.
1959
Fred Cass's name appears on the cover as the new Minister of the Department of Highways
1960
Lithography changed to Rolph-Clark-Stone Ltd.
The Ontario coat of arms is placed against the white silhouette of a King's Highway sign on the cover for the first time.
1961
 
1962
John Robarts's name appears on the cover as the new Premier of the Province
W. A. Goodfellow's name appears on the cover as the new Minister of the Department of Highways
Highway numbering reaches 136
1963
Map dimensions changed - closed dimensions remained the same.  Opened dimensions changed from 41" W X 25" H to 36.5 W" X 25". 
The mileage tables, which had been used since the 1920's were removed and replaced by the mileage chart.
Regulatory sign area was redesigned.
Trillium in the oval - provincial logo - makes it's debut on a cover.
The yellow tinge was removed as the main background color of the map of Ontario
Reference markings around the perimeter of the map were made alternating colors for ease of use.
Blue border on the rear cover was removed.
C. S. McNaughton's name appears on the cover as the new Minister of the Department of Highways
Garden City Skyway in St. Catharines opens to traffic.
1964
 
1965
Counties and districts became more easily distinguished as they were colored differently from each other.
Last year that the boxed safety slogans are included on the map in areas of water.
Highway 401 is named the "McDonald-Cartier Freeway" to honor two of Canada's founding fathers.
1966
A new folding system was incorporated where locating communities on the map became much easier thanks to indexing letters which were visible immediately after open the first two folds.
The back cover had an "Instructions For the Use of Map" area and small key maps were included as well.
1967
George Gomme's name appears on the cover as the new Minister of the Department of Highways
1968
Colored drawings of the ships by the grain elevator and the tractor pulling the combine which had been used on the cover of the 1962 Official Ontario Road Map were reused on this year's cover.
The last section of Highway 401 is completed from Ivy Lea Bridge to Brockville.
1969
The official flower of Ontario - the Trillium, is stylized into a logo and included for the first time on the cover, replacing the Ontario coats of arms in a white outlined of a King's Highway sign.
1970
A map showing Ontario in relation to neighboring provinces and states is expanded for the first time to show Ontario's relation to all of Canada and most of the United States.
1971
The amount of Northern Ontario shown is expanded northwards to include a small portion of Hudson Bay - the District if Kenora is included. 
Indexing the names of lakes in Northern and Southern Ontario was discontinued.
Premier William Davis's name appears for the first time on the cover of the map.
Charles McNaughton's name re-appears on the cover as the Minister of the Department of Highways
The Department of Highways and the Department of Transport were amalgamated to form the Department of Transportation and Communication.
1972
The Department of Transportation and Communications was renamed the Ministry of Transportation and Communications on April 1st.
1973
First official road map issued by the Ministry of Transportation and Communications (MTC) - replacing the old name of the Department of Highways.
Toll collection on the Darden City Skyway and Burlington Skyway is discontinued.
1974
In 1974 the practice of coloring counties different colors started in 1965 was discontinued.
John Rhodes's name appears as the new Minister of the Ministry of Transportation and Communications.
First reference to kilometres in the map - dual distance scale begun
1975
 
1976
 
1977
Mileage Chart name changed to "Distance Triangle"
James Snow's name appears as the new Minister of the Ministry of Transportation and Communications.
1978 - 1979
First bilingual - English and French map.
1980
First cover using the "Ontario - Yours to Discover" promotional slogan with the Ontario flag incorporated into the word "Ontario"
1981
First year of the map having a white cover with smaller photograph - the modern standard for the cover.
1982
 
1983
 
1984 - 1985
Last year that "Instructions For the Use of the Map" were placed on the rear.  In subsequent years - the maps were folded differently with the top edge of the cover not being a folded edge, but rather - an open edge.
1986 - 1987
Major revision occurred with this issue. 
This was the first year since 1976 that the folded map was smaller - 4.75" width - reduced from 5.25 and height - 9.75" reduced from a 10" height. 
The clear indexing feature of the partially opened map, introduced in 1966, was discontinued, however the map was still folded in the same manner. 
The enlarged view of South Central Ontario was also discontinued.  The Index of Cities, Towns and Villages was renamed the "Settlement Index". 
List of radio stations was discontinued. 
The legend was placed on the third fold of the cover and the "Instructions For Use of the Map", were discontinued.
David Peterson's name appears on the cover as the new Premier.
Ed Fulton's name appears as the new Minister of the Ministry of Transportation and Communications.
The Ministry of Transportation and Communications was renamed the Ministry of Transportation following the transfer of the Communications Division to the new Ministry of Culture and Communications in September 1987
1988 - 1989
Coloring was added to the Distance Triangle to make it easier to locate distances. 
Small maps of Ontario were added to each side of the map to illustrate the scale being used.
First map cover to use the "Ontario Incredible" promotional slogan
1990 - 1991
Premier's, Minister's and Deputy Minister's names are not included on the map cover for the first time in their history.
Ontario Provincial Police contact information was removed from both sides of the map and added to the bottom of the legend.
Radio station information re-appears on the map.
First proclamation on the cover of the map being reprinted on re-cycled paper
The "Ontario Incredible" slogan is discontinued
1992 -1993
Traffic Signs were removed from the back of the map and replaced by the Ministry of Transportation Safety Tips
A new promotional heading is used on the cover in conjunction with other Ontario tourism efforts - the word "Ontario" with a colored leaf between the A and R.
1994 - 1995
First issues to have a price shown on the cover. 
The Ministry of Transportation and Communications name is changed to the Ministry of Transportation. 
Safety tips on the rear cover have changed slightly from the 1992/93 issue.
1996
More area is provided for the legend and the OPP information is added in below the Safety Tips area.
1997
 
1998
The province transfers ownership of many King's Highways to local municipalities.
1999
A '1-800" number is used for the first time on the cover.
2000
 
2001
The location used for the cover photograph was also used on the cover of the 1992/93 Official Road Map.
The same photograph on this cover had been used previously as one of the small photographs on the cover of the 1999 Official Map.
The promotional heading used on the cover - the word "Ontario" with a colored leaf between the A and R is discontinued.
2003
The inclusion of a small Ontario Provincial flag begins on the cover.
2005
Advertising is included in the Official Ontario road map for the first time.
2006
 
2014-2015
 Removal of Radio Station listings.  Addition of Roundabout Info