ST. CHARLES — Boeing Co. plans a $70 million expansion of its missile and munitions plant on the city’s north side, aided by about $18 million in property tax abatement expected to be approved by city officials.

Sarah Reed, a Boeing spokeswoman, said the company currently doesn’t expect to add any employees at the St. Charles site because of the expansion.

However, she said, “it’s going to secure production and operation and a skilled workforce at the site now and in the future.”

Reed said the tax abatement would be spread over 20 years. No county or state incentives are being provided, she said.

She said a new building would be constructed on the northeast corner of its existing plant site. Groundbreaking likely will take place later this year and completion is expected by 2021.