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The US is believed to have spent $800m (£554m) on radar and SM-2 missile interceptors since 2013.
The station will have a battery of SM-2 missile interceptors.
Nato and US officials say the system has been developed to track and intercept missiles fired from a "rogue" state. In the past Iran was mentioned in that context, but the US has also had North Korea in mind.
For years the US has been testing the Aegis system on warships too.
The officials also stress the shield is not directed against Russia.
"Both the US and Nato have made it clear the system is not designed for or capable of undermining Russia's strategic deterrence capability," US Assistant Secretary of State Frank Rose said on Wednesday.
"Russia has repeatedly raised concerns that the US and Nato defence are directed against Russia and represents a threat to its strategic nuclear deterrent. Nothing could be further from the truth," he added.
Russia's foreign ministry warned on Wednesday that the system violated a treaty on nuclear forces.
A ministry statement quoted by Interfax news agency said it was a breach of the Intermediate-Range Nuclear Forces (INF) Treaty, signed in 1987.
"This decision is harmful and mistaken, because it is capable of upsetting strategic stability," said Mikhail Ulyanov, head of the Russian foreign ministry's department for proliferation and arms control issues.
An incoming missile would be destroyed in space, before it could re-enter the Earth's atmosphere.
On Friday, another phase of the project will be launched in Poland with a groundbreaking ceremony at Redzikowo, near the Baltic Sea. Aegis missiles are to become operational there in 2018.
Mr Ulyanov said Russia's interests "are being affected in a direct way by this".
He said the Americans' MK-41 launch system could also be used to fire cruise missiles, not just air defence missiles.
"From our viewpoint this is a violation of the Intermediate-Range Nuclear Forces Treaty," he said.