The judicial power of the state shall be vested in the senate sitting as a court of impeachment, a supreme court, circuit courts, chancery courts, courts of probate, such courts of law and equity inferior to the supreme court, and to consist of not more than five members, as the legislature from time to time may establish, and such persons as may be by law invested with powers of a judicial nature; but no court of general jurisdiction, at law or in equity, or both, shall hereafter be established in and for any one county having a population of less than twenty thousand, according to the next preceding federal census, and property assessed for taxation at a less valuation than three million five hundred thousand dollars.