World Guide Covered Bridge (WGCB) numbers have been assigned by the National Society for the Preservation of Covered Bridges (NSPCB) are referenced for all listed bridges.  Assigned numbers are coded, such as NH-05-12 or VT-115-a.  The first two characters are the postal abbreviations for the state (formerly digits starting at 01 represented the state in alphabetical order).  The second two digits represents the county in alphabetical order starting at 01 for each state.  The third pair of characters represents the bridges place in the NSPCB tally of that county's bridges, starting at 01 for authentic truss type bridges or a letter for non-authentic type bridges, an upper case letter for motor vehicle bridges, and a lower case letter for footbridges.  Additionally, bridges that have a leading "(" before the last letter, are considered O.C.B.I. - "Of Covered Bridge Interest" - a Covered Bridge that is under 12' or is just on the ground and not over anything, i.e., 45-12-(b.

Maine - General information. At one time Maine had about 120 covered bridges. Most of these were located within the southwestern part of the state. Today, six of the surviving historic covered bridges are still located in the same area, with two in the south central area, and one in the far northeast. That covered bridge located the farthest north of any covered bridge in the United States. In addition to the historic spans, six more recent structures have been built, four in the later part of the twentieth century and two as recently as 2000 and 2001. Records indicate that the earliest covered bridge was built in the city of Augusta. Maine in 1819.