The morphotropic phase boundary (MPB) has been recently extended from ferroelectrics to ferromagnets, especially for giant magnetostrictive materials. The giant magnetostrictive system in turn presents abundant research opportunities on MPB investigation. In this work, we demonstrate that a magnetic-ordering tricritical type MPB near room temperature can be constructed in the TbxHo1−x(Fe0.9Co0.1)2 magnetostrictive system. An ultrahigh magnetostrictive sensitivity is obtained that achieves the performance of the commercial Tb0.27Dy0.73Fe2 (Terfenol-D) polycrystal in the Tb0.2Ho0.8(Fe0.9Co0.1)2 alloy. The detailed domain microstructures near the magnetic-ordering tricritical region are determined using phase-field simulations. Our results provide the underlying insights of magnetic-ordering tricritical MPB needed to guide the design of ultrasensitive magnetostrictive materials.