How many persons are there in the Godhead?

There be three persons in the Godhead, the Father, the Son, and the Holy Ghost; and these three are one true, eternal God, the same in substance, equal in power and glory; although distinguished by their personal properties.[1]

1. Matt. 3:16-17

   And when Jesus was baptized, immediately he went up from the water, and behold, the heavens were opened to him,  and he saw the Spirit of God descending like a dove and coming to rest on him; and behold, a voice from heaven said, “This is my beloved Son,  with whom I am well pleased.”

   
   Matthew 28:19

   Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit...

   II Cor. 13:14

   The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all.

   John 10:30

   I and the Father are one.

Westminster Larger Catechism, Question 9. Scripture quoted from the ESV.