Employees said that the gun went off as the woman carrying it set her purse down on the counter, The Kansas City Star reported. It fired again as she fled the office with a male companion.
The Health Department's customer service desk was closed for about two hours.
The wounded woman declined medical attention after paramedics examined the wound, police said. Investigators were trying to find the woman with the gun and the man with her and to determine if they had broken any laws.