Edward Hospital & Health Services and Elmhurst (Ill.) Memorial Healthcare have signed a definitive agreement to merge, a move by Edward CEO Pam Davis to create one of the largest hospital systems in the Chicago area, with total revenue of about $1 billion.

The announcement today comes nearly three months after the two west suburban systems signed a letter of intent to consolidate.

They announced the agreement in a notice that was filed on the website of the Municipal Securities Rulemaking Board, which distributes disclosure statements to bondholders.

Davis would lead the new system, which would include 259-bed Elmhurst, 309-bed Edward and 108-bed Linden Oaks, a behavioral health hospital Naperville-based Edward operates.

Elmhurst CEO W. Peter Daniels unexpectedly resigned late last month, apparently as the two sides were putting the finishing touches on the merger agreement.

Now, the hard work of the merger really starts.

Leaders from both systems have started to work on transition plans, according to a separate news release, including how to grow existing services and add locations while creating efficiencies amid shrinking reimbursements from payers, such as insurance companies and the federal government.

The merger is slated to be completed this summer.

The Federal Trade Commission's preliminary antitrust review period of the merger has elapsed, the release said. The proposed deal still must be approved by the Illinois Health Facilities and Services Review Board, which reviews health care construction and ownership changes to prevent duplicating services.

A spokesman for Edward said he didn't have anything to add beyond the statement. A spokeswoman for Elmhurst did not immediately return a message to comment.