A. J. (Alexander Jackson) Davis forms the first recognizably modern architectural office in partnership with Ithiel Town.

Davis had dropped out of school to become a respectable lithographer after studying at the American Academy of Fine Arts, the New-York Drawing Association, and from the Antique casts of the National Academy of Design.

He had made a first independent career as an architectural illustrator in the early 1820s, but his friends, especially the painter John Trumbull, had convinced the young man to turn his hand to designing buildings.

In 1826 he had gone to work as a draftsman for New York architect Josiah R. Brady, an early exponent of the Gothic revival. (Brady's Gothic 1824 St. Luke's Episcopal Church is the oldest surviving structure in Rochester, New York.)

Davis had soon left to work in the most prestigious architectural firm of the Greek Revival, the office of Ithiel Town and Martin E. Thompson; here, Davis had had access to the best architectural library in the country, and had gained a thorough grounding in this congenial atmosphere.

Picturesque siting, massing, and contrasts remain essential to the work of A. J. Davis, even when he is building in a Classical style.

With Ithiel Town's partner James Dakin, he designs the noble colossal Corinthian order of "Colonnade Row" on New York's Lafayette Street, the very first apartments designed for the prosperous American middle class (1833; half still stand today, across from the Public Theater).

Davis has also designed the Custom House of New York City, on which construction had begun in 1833.

A. J. Davis has designed many late classical buildings, including some of public prominence.

In Washington, Davis has designed the Executive Department offices and the first Patent Office building (1834).

In 1831 he had been elected an associate member of the National Academy and had been one of three architects who established the American Institute of Architects in May, 1837. (He will resign in his retirement years, believing the A.I.A. had strayed from its original purpose.)

None of a series of A.J. Davis's consultations over state capitols have apparently resulted in buildings entirely as he had planned: the Indiana State House, Indianapolis (1831 – 35) had elicited calls for his advice and designs in building other state capitols in the 1830s.

Davis's North Carolina's statehouse (1833 -40, with local architect David Paton), ...

...the Illinois State Capitol, often attributed entirely to the Springfield, Illinois architect John Rague, who was at work on the Iowa State Capitol at the same time, and ...

...the committee responsible for commissioning a design for the Ohio Statehouse asks Davis's advice in 1839.

The resulting capitol in Columbus, Ohio, often attributed to the Hudson River Valley painter Thomas Cole consulting with Davis and Ithiel Town, has a stark Greek Doric colonnade across a recessed entrance, flanked by recessed window bays that continue the rhythm of the central portico, all under a unique drum capped by a low saucer dome. (Davis will continue in partnership with Town until shortly before Town's death in 1844.)

Davis had begun work in 1835 on his own on his only publication, Rural Residences, the first pattern book for picturesque residences in a domesticated Gothic Revival taste, which can be executed in carpentry, and also contained the first of the "Tuscan" villas, flat-roofed with wide overhanging eaves and picturesque corner towers.

Unfortunately, the Panic of 1837 had cut short his plans for a series of like volumes, but Davis had soon formed a partnership with Andrew Jackson Downing, illustrating his widely read books.