This paper presents the results of 16 years of monitoring stellar orbits around the massive black hole in the Galactic Center (Sgr A*) using high-resolution near-infrared techniques. The study improves upon previous analyses by enhancing the coordinate system definition, achieving long-term astrometric accuracy of ~300 μas, and thoroughly investigating systematic error contributions. Using this data, the orbits of 28 stars, including S2, were determined. S2 has completed a full orbit since monitoring began. The results show that all stellar orbits fit well with a single point mass potential, with astrometric uncertainties now ~6× better than previous studies. The mass of the central object is (4.31±0.06|stat±0.36|R0)×10^6 M☉, with the main uncertainty due to R0. The current best estimate for R0 is 8.33±0.35 kpc. The mass scales with distance as (3.95±0.06)×10^6 (R0/8 kpc)^2.19 M☉. The orientations of orbital angular momenta for stars in the central arcsecond are random. Six stars are identified as late-type, and six as early-type members of the clockwise rotating disk system. The mass enclosed between the pericenter and apocenter of S2 is less than 0.066 times the mass of Sgr A* at 99% confidence. This is two orders of magnitude larger than expected from other estimates. The study provides a detailed analysis of astrometric data, including calibration of reference stars, cross-calibration with SiO maser stars, and the construction of a combined coordinate system. The final coordinate system has an accuracy of ~1.0 mas in position and ~0.1 mas/yr in velocity. The results confirm the existence of a massive black hole at the Galactic Center and provide insights into the dynamics of stars in its vicinity.This paper presents the results of 16 years of monitoring stellar orbits around the massive black hole in the Galactic Center (Sgr A*) using high-resolution near-infrared techniques. The study improves upon previous analyses by enhancing the coordinate system definition, achieving long-term astrometric accuracy of ~300 μas, and thoroughly investigating systematic error contributions. Using this data, the orbits of 28 stars, including S2, were determined. S2 has completed a full orbit since monitoring began. The results show that all stellar orbits fit well with a single point mass potential, with astrometric uncertainties now ~6× better than previous studies. The mass of the central object is (4.31±0.06|stat±0.36|R0)×10^6 M☉, with the main uncertainty due to R0. The current best estimate for R0 is 8.33±0.35 kpc. The mass scales with distance as (3.95±0.06)×10^6 (R0/8 kpc)^2.19 M☉. The orientations of orbital angular momenta for stars in the central arcsecond are random. Six stars are identified as late-type, and six as early-type members of the clockwise rotating disk system. The mass enclosed between the pericenter and apocenter of S2 is less than 0.066 times the mass of Sgr A* at 99% confidence. This is two orders of magnitude larger than expected from other estimates. The study provides a detailed analysis of astrometric data, including calibration of reference stars, cross-calibration with SiO maser stars, and the construction of a combined coordinate system. The final coordinate system has an accuracy of ~1.0 mas in position and ~0.1 mas/yr in velocity. The results confirm the existence of a massive black hole at the Galactic Center and provide insights into the dynamics of stars in its vicinity.