The boost contributes to the longer-term trend, which has seen property prices in the area achieve 5.6% annual growth – the highest in the North East.
The average Northumberland house price in June was £160,052, Land Registry figures show – a 2.5% increase on May.
Over the month, the picture was similar to that across the North East, where prices increased 2.9%, but Northumberland easily outperformed the 0.7% rise for the UK as a whole.
Over the last year, the average sale price of property in Northumberland has risen by £8,500.
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That increase puts the area top among the North East’s 12 local authorities for annual house price growth.
The most expensive properties in the North East were in North Tyneside – where the average was £164,000.
At the other end of the scale, properties in Middlesbrough dropped 8.3% in value, giving an average price of £103,000.
Owners of semi-detached houses saw the biggest improvement in property prices in Northumberland in June – they increased 2.6%, to £151,740 on average.
Over the last year, prices have risen by 5.7%.
The price of detached homes in the county were up by 2.4% on the month – and up 6.6% annually to an average of £269,027.
The value of terraced homes also rose – up 2.5% monthly to an average of £125.259 and 5.3% up on prices at the same time last year.
Flat owners saw the price of their property rise by 2.1% between May and June – up 2.4% annually to an average of £85,831.
First-time buyers in Northumberland spent an average of £130,300 on their property – £6,500 more than a year ago, and £13,000 more than in June 2015.
Buyers paid 21.5% more than the average price in the North East – £132,000 – in June for a property in Northumberland.
Across the North East, property prices remained relatively low compared to those across the UK – where the average cost was £238,000.
The highest property prices in the country were in Kensington and Chelsea, in London, where the average June sale price was £1.4m.