The council purchased the Shrewsbury's Darwin Shopping Centre, the Pride Hill Shopping Centre and the lease on the Riverside Shopping Centre along with the Riverside Medical Practice last year.
The deal was worth £51m but now the council has confirmed their value has dropped by around a fifth.
Councillor Peter Nutting, the council's leader, said he is not concerned at the valuation, and says the centres were bought to support the future of the town.
He said: "We knew that the tenancies, income and value would change, but we bought them as an investment to support the economic growth and future vitality of the town centre, as well as provide us with a sustainable year-on-year income stream. This hasn’t changed.
“The outlook in the short-term suggests that income will fall before it rises, but we were prepared for that and we knew it would still be making us money and helping to pay for essential public services across the county.
“Footfall is good and the town centre continues to buck the national trend. This is not only great for Shrewsbury, but also for the rest of the county as it encourages tourism and provides jobs.”
As well as revealing the valuation of the centres, the council has also confirmed when work will begin on refurbishing the next section of the Darwin Centre.
The work, on the middle level of the centre, is due to start in the autumn, and will include new flooring, lighting and ceiling design, along with the refurbishment of the public toilets.
It follows improvements to the upper and lower levels under the previous owner in 2017, and is part of the council’s long-term plans to improve and further develop the shopping centres it bought in January 2018.
Councillor Nutting said: “When we bought the centres, we put aside £4 million from our capital budget to make essential improvements to the Darwin Shopping Centre, particularly the lower and middle levels. It’s part of our business plan.
“We know that making these improvements will create a better environment for shoppers and help us to continue to attract and retain an excellent mix of retail and leisure.”
A spokesman for the authority said that since buying the centres, the council has been working hard to increase footfall.
He said they are "performing well, and securing a number of national and independent stores has meant that vacancy rates continue to remain low".