A year later, he was in Phoenix where he built what is claimed to be Phoenix's second house.
He was one of the first builders in the area, using adobe techniques suited for the available materials.

In 1870, he was a signatory to the formation of the Salt River Valley Town Association, the first government of the area that became Phoenix.
On January 17, 1871, he planted the first Cottonwood tree in the town.

He partnered with Captain Hancock in 1871 to erect the first Maricopa County Courthouse which they rented to the county as the seat of the county government.
The city's first public school was located there and the first District Court for Maricopa County held its initial session in the building which also acted as the civic center of the city.
When the county moved out in 1875, the building was used as a Justice of the Peace office for many years.

In May 1872, he built a barn and corral for the Starar Brothers, from which they ran the Phoenix Livery, Feed, and Sales Stables on the corner of Washington Street and First Avenue.
 Monihon was paid with a one-third ownership interest in the business.
At some point, Monihon bought out his partners and became sole owner.
He operated the business for ten years.

He was on the board of supervisors in 1874, and was nominated to run in the first mayoral election as the Republican candidate after Phoenix was incorporated in 1881.
He lost by seven votes but was elected councilman the next year.

He left Phoenix for a period of six years but returned from the east in 1889 and became chairman of the board of directors of the Insane Asylum of Phoenix which had opened two years earlier.

The next year, he built a large building on part of the stable grounds.
The Monihon building was at the time considered "the finest edifice in Arizona".
It was torn down in the mid-1930s.
A year later, he was in Phoenix where he built what is claimed to be Phoenix's second house. He was one of the first builders in the area, using adobe techniques suited for the available materials.
In 1870, he was a signatory to the formation of the Salt River Valley Town Association, the first government of the area that became Phoenix. On January 17, 1871, he planted the first Cottonwood tree in the town.
He partnered with Captain Hancock in 1871 to erect the first Maricopa County Courthouse which they rented to the county as the seat of the county government. The city's first public school was located there and the first District Court for Maricopa County held its initial session in the building which also acted as the civic center of the city. When the county moved out in 1875, the building was used as a Justice of the Peace office for many years.
In May 1872, he built a barn and corral for the Starar Brothers, from which they ran the Phoenix Livery, Feed, and Sales Stables on the corner of Washington Street and First Avenue.  Monihon was paid with a one-third ownership interest in the business. At some point, Monihon bought out his partners and became sole owner. He operated the business for ten years.
He was on the board of supervisors in 1874, and was nominated to run in the first mayoral election as the Republican candidate after Phoenix was incorporated in 1881. He lost by seven votes but was elected councilman the next year.
He left Phoenix for a period of six years but returned from the east in 1889 and became chairman of the board of directors of the Insane Asylum of Phoenix which had opened two years earlier.
The next year, he built a large building on part of the stable grounds. The Monihon building was at the time considered "the finest edifice in Arizona". It was torn down in the mid-1930s.
James D. Monihon