No unambiguous statement from Joseph Smith has been found stating that he believed in the Trinity as described in Christian dogma in 1829 or at any time thereafter. Claims that Joseph Smith’s concept of God evolved between 1829 and 1838 ignore plain evidences showing it did not.

Consider these examples:

1829

In the Book of Mormon speaks of one [Christ] followed by twelve others descends from God to speak with Lehi--thus, Jesus and the Father are here both separate (1 Nephi 1:8-10).

After descending to the Nephites, the Savior taught them many lessons (3 Nephi 11-16) then he told them:  “Now I go unto the Father” (3 Nephi 17:4). This is a plain declaration of the physical separateness of Christ and the Father. They importuned him to stay, which he did.

Jesus prayed in front of the Nephites saying "Father, I am troubled because of the wickedness of the people of the house of Israel." The text continues:  "Behold he prayed unto the Father, and the things which he prayed cannot be written and the multitude did bear reacord who heard him" (3 Nephi 17:14-15). None of the Nephites would have believed that Christ and the Father were the same being or essence as described in the Trinity dogma. Neither does the Book of Mormon teach that doctrine.

1830

Book of Moses: "And I have a work for thee, Moses, my son; and thou art in the similitude of mine Only Begotten" (Moses 1:2-6).

Book of Moses:

"And he called upon our father Adam by his own voice, saying: I am God; I made the world, and men before they were in the flesh. And he also said unto him: If thou wilt turn unto me, and hearken unto my voice, and believe, and repent of all thy transgressions, and be baptized, even in water, in the name of mine Only Begotten Son, who is full of grace and truth, which is Jesus Christ, the only name which shall be given under heaven, whereby salvation shall come unto the children of men, ye shall receive the gift of the Holy Ghost, asking all things in his name, and whatsoever ye shall ask, it shall be given you" (Moses 6:51-52).

On September 26, 1830 Joseph dictated D&C 29:27: 

"And the righteous shall be gathered on my right hand unto eternal life; and the wicked on my left hand will I be ashamed to own before the Father."

1831

John Whitmer recorded that Joseph "saw the heavens opened, and the Son of Man sitting on the right hand of the Father" during the June 3, 1831 general conference. Of this same experience, Levi Hancock wrote: “Joseph Smith then stepped out onto the floor and said, 'I now see God, and Jesus Christ at his right hand, let them kill me, I should not feel death as I am now.'”

D&C 45:3 dictated March 7, 1831 depicts a complete separateness of Christ and the Father: 

"Listen to him who is the advocate with the Father, who is pleading your cause before him-- Saying: Father, behold the sufferings and death of him who did no sin, in whom thou wast well pleased; behold the blood of thy Son which was shed, the blood of him whom thou gavest that thyself might be glorified;Wherefore, Father, spare these my brethren that believe on my name, that they may come unto me and have everlasting life" (D&C 45:3-5).

1832

On February 16, 1832, Joseph Smith and Sidney Rigdon received a revelation of the three degrees of glory and declared:

“And now, after the many testimonies which have been given of him, this is the testimony, last of all which we give of him: That he lives! For we saw him, even on the right hand of God; and we heard the voice bearing record that he is the Only Begotten of the Father” (D&C 76:22-23; bold added).

The preface of the 1832 account of the First Vision states:

“History of the life of Joseph Smith Jr. an account of his marvilous experience1 and of all the mighty acts  which he doeth in the name of Jesus Ch[r]ist the son  of the living God.” The vision account ends with: “behold and lo I come quickly as it [is] wr itten of me in the cloud <clothed> in the glory of my Father.” The clear implication is that Christ and the Father are two separate Beings.

1832–1833

—Two of Joseph's close associates reported their own visions of deity with clearly separate divine beings, the Father and the Son.

Zebedee Coltrin (Member of the School of the Prophets)

At one of these meetings after the organization of the school, (the school being organized on the 23rd of January, 1833) when we were all together, Joseph having given instructions, and while engaged in silent prayer, kneeling, with our hands uplifted each one praying in silence, no one whispered above his breath, a personage walked through the room from east to west, and Joseph asked if we saw him. I saw him and suppose the others did and Joseph answered "that is Jesus, the Son of God, our elder brother." Afterward Joseph told us to resume our former position in prayer, which we did. Another person came through; he was surrounded as with a flame of fire. [I] experienced a sensation that it might destroy the tabernacle as it was of consuming fire of great brightness. The Prophet Joseph said this was the Father of our Lord Jesus Christ. I saw Him.

[When asked about the kind of clothing the Father had on, Brother Coltrin said:] I did not discover his clothing for he was surrounded as with a flame of fire, which was so brilliant that I could not discover anything else but his person. I saw his hands, his legs, his feet, his eyes, nose, mouth, head and body in the shape and form of a perfect man. He sat in a chair as a man would sit in a chair, but this appearance was so grand and overwhelming that it seemed I should melt down in his presence, and the sensation was so powerful that it thrilled through my whole system and I felt it in the marrow of my bones. The Prophet Joseph said: "Brethren, now you are prepared to be the apostles of Jesus Christ, for you have seen both the Father and the Son and know that they exist and that they are two separate personages."...

The school room was in the upper room of [Newel K.] Whitney's store. ("Statement of Zebedee Coltrin,"

Minutes, 3 October 1883, Salt Lake School of Prophets, LDS Church Archives, Salt Lake City, Utah, 56-58; see also Lyndon W. Cook, The Revelations of the Prophet Joseph Smith (Salt Lake City, Utah: Deseret Book, 1981), 187-88)

John Murdock:

During the winter that I boarded with[Bro[ther] Joseph... we had a number of prayer meetings, in the Prophet’s chamber.... In one of those meetings the Prophet told us if we could humble ourselves before God, and exersise [sic] strong faith, we should see the face of the Lord. And about midday the visions of my mind were opened, and the eyes of my understanding were enlightened, and I saw the form of a man, most lovely, the visage of his face was sound and fair as the sun. His hair a bright silver grey, curled in a most majestic form, His eyes a keen penetrating blue, and the skin of his neck a most beautiful white and he was covered from the neck to the feet with a loose garment, pure white, whiter than any garment I had ever before seen. His countenance was the most penetrating, and yet most lovely. And while I was endeavoring to comprehend the whole personage from head to feet it slipped from me, and the vision was closed up. But it left on my mind the impression of love, for months, that I never felt before to that degree.(John Murdock, autobiography and diary, 13, L. Tom Perry Special Collections, Harold B. Lee Library, Brigham Young University, Provo, Utah).

Also later references to "one God" can be found that apparently caused no stir. On March 15, 1844, the Times and Seasons  published a reference: "There is one God who presides over the destinies of all nations and individuals, both religiously and politically, and numbers of the hairs of all our heads." The editors apparently saw no problem.