And making them suitable for all vehicles would cost the council an estimated Â£25.9 million.
Transport experts say widespread improvement of roads and bridges is desperately needed but severely underfunded.
Out of 972 council-run bridges in the area, 80 are in poor condition and have been categorised as substandard, according to analysis by the RAC Foundation.
That means they are unable to bear the weight of the heaviest vehicles on the road.
Some are substandard because they were built to earlier design standards, while others may have deteriorated through age and use.
Many of these weaker bridges will be subject to weight restrictions, or written off altogether if the local authority decides they aren't repairing it.
Northumberland County Council said that if it had no budget restrictions, it would like to bring 72 of these bridges back up to full carrying capacity.
But budget constraints mean it anticipates only twenty-five bridges having the necessary work done within the next five years.
Clearing the backlog of repairs for all the bridges in the area would cost the council Â£200 million .
The analysis was carried out in partnership with the National Bridges Group of ADEPT, a group representing local authority leaders.
RAC Foundation director Steve Gooding described the findings as "worrying".
He said: “Establishing the condition of our highway bridges provides a litmus test for the condition of our road network.
"The headline message is that councils nationally are facing severe underfunding for all aspects of road maintenance, not just to fill in potholes.
“We should all be concerned when bridges along major routes are not able to carry the heaviest vehicles on the road. Many thousands are subject to enhanced monitoring, speed and weight restrictions, and the cost of bringing them up to scratch is continuing to mount.
“Longer term, the growing maintenance backlog risks pushing more and more bridges into the most worrisome category."
The RAC Foundation estimated that it would cost Â£6.7 billion to clear the backlog of repairs for Britain's bridges.
Local Government Association transport expert Martin Tett said the study "underlines the chronic need for more investment in existing local roads".
He said: "While the extra one-off Â£420 million funding announced in the Budget will help, only long-term, consistent and fairer government investment in local road maintenance can allow councils to embark on the widespread improvement of our roads and bridges that is desperately needed."