Royal Banks of Missouri in University City has agreed to buy Frontenac Bank in Earth City, Mo.
The companies did not disclose the price of the deal, which is expected to close in the second quarter.
Steve Baden, the $415 million-asset Royal's president, will keep that title. Robert Roberson, the $285 million-asset Frontenac's chairman and chief executive, will oversee financial and administrative matters.
The company's board will have directors from both banks.
Royal has five branches around St. Louis; Frontenac has four branches in the area. Royal said it plans to keep all offices open.
Sandler O'Neill and Polsinelli advised Royal. Sheshunoff & Co. and Lewis Rice advised Frontenac.