The 11th of January has always been a day of milestones for Cook County Circuit Judge William D. Maddux. On that day in 1886, his father was born. In 1960, it was his first day as a lawyer at Kirkland & Ellis LLP. And in 1991, on that same day, he took the oath to join the Cook County bench. It’s only fitting then, Maddux said, to walk away and retire on Jan. 11. At age 78, Maddux will leave on his own timing — and much to his own credit. Before his most recent term began, he filed a lawsuit to …