Following the close of the Civil War he moved to Chicago, opened an office there in 1876, and the following year built the first large apartment house in the city.
During the early eighties he joined Alfred Pashley (then in his twenties) in partnership (Willett & Pashley), and soon acquired a large practice. Commissioned architects of a Hospital for the Insane at Kankakee, Ill., the partners adapted the so-called “cottage" plan for the building, and as the first architects to modernize hospital planning, won wide recognition. Later they designed buildings of the same type in Iowa and North Dakota.
In Chicago the firm did extensive work for the Roman Catholic Archbishop reehan, designing the Holy Cross Cathedral, many churches and schools in the Diocese, and in addition city and county residences for the Archbishop. Among the secular buildings planned by Willett & Pashley was the College of Dental Surgery built in 1892, also several business blocks in the city, factory buildings, and residences in many localities.
A well known early architect in Chicago, Mr. Willett was one of the organizers of the Chicago Chapter in 1869, and during the following year was elected to the A.I.A.