The major doctrines of both will be the same. The churches who use the name "First Baptist" are usually either Southern Baptist, or American Baptist. The biggest thing you would notice are the type of music they use in services. Southern Baptists like contemporary Christian music, and I've even seen Pastors playing bass guitars in their services. Ive never been to an American Baptist church, but understand they are heavily African American. The music you'd hear there would be most likely soul and gospel sang in that manner. I personally like that music very much. You will likely find after looking deeper that they will have slightly different views on separation from non believers, and reformation churches. The Southern Baptists a few years ago, were very ecumenical, however that is changing. The American Baptists, Ive been told are ecumenical also, but I don't know that for fact. Another difference will be readily apparent. The Bible used in the services. The more liberal churches of both flavors will use either the NIV or ASV. The conservatives, myself included, will use the KJV.

It is my understanding that the name "First Baptist" indicates only chronology. The first group of Baptists to start meeting in a given place often called their congregation the first Baptist Church of <city/place>. It is likely true that this will be an affiliate of one of the larger Baptist denominations (e.g. Southern or American) because there are more of them and they were more likely to be the first Baptist congregation in a given place. I think I have occasionally run across a "Second Baptist" church of wherever, indicating that they were the, well, um... second Baptist church started in wherever.

Found this on another site, it was a very good explanation: Short Answer: First Baptist Churches just mean that they were the First Baptist Church to set up in a particular town, city or area. A First Baptist could belong to the Southern Baptist Convention, American Baptist Convention, or one of the other smaller conventions. They could also be independent. A Southern Baptist Church is a church that belongs to the Southern Baptist Convention, the largest of the Baptist Conventions. Long Answer:In the US, Baptist constitute 27 groupings and their total membership is about 30 million. Baptist churches are completely independent, yet bound together by an amazing common allegiance to principles and doctrines. They claim no founder but Christ, and often claim they have been preaching since John the Baptist. When the Reformation began in the 16th century, scattered Baptist groups in Europe advocated doctrines that eventually united them. As the left wing of the Reformation, they were called ANA-Baptists ("to baptize again"), because they immersed (dunked) those who had been baptized in infancy. They held to a literal application of the Bible, were communal and pacifistic, and opposed capital punishment, taking oaths in court, and the holding of public office. They insisted upon the complete separation of church and state. Undergoing persecution for their then - radical views, they spread all over Europe. In Holland a group of Mennonites, followers of the former Anabaptist leader Menno Simons, were teaching Anabaptist principles and took in a group of British refugees undergoing persecution under James I. One of their leaders, John Smyth, completely accepted the teaching of the Mennonites. Smyth and his followers were rebaptized, became Anabaptists, and organized the first English Baptist church in 1609. However, they remained English and refused to take on all the accoutrements of the Mennonites. As persecution waned, the English Baptists went back across the channel and began a Baptist church in London. Although they spread, they divided again, this time over the theology of the Atonement. The General Baptist churches held that Jesus Christ died for everyone, while others held to the teachings of the Particular Baptist church - following the teachings of John Calvin - that salvation was only for those predestined by God. The first Particular (British) Baptist Church had its beginning in 1638. A third group, Immersion Baptist, broke away and in 1644 produced a confession of faith that is still in use by many. For the first time, these Christians were popularly known as Baptists. In 1631 Roger Williams went to America, and although he was not a Baptist, established a Baptist church at Providence, RI. In 1814 Baptists organized the General Missionary Convention of the Baptist Denomination in the United States of America for Foreign Missions. This step marked the first real denominational consciousness and united the Baptists. They formed a society for publication as well as for missions and education. In 1845 came the major split. Southerners seceded from the union over the issue of slavery and state’s rights, and formed the Southern Baptist Convention to carry on the work of their churches. What was left of the General Missionary Convention formed the Northern Baptist Convention which changed its name to American Baptists Churches USA. The two have remained separated ever since. Baptists generally agree upon the Bible as the inspired Word of God, the supremacy of Jesus Christ, inherent freedom of individuals to approach God for themselves, salvation by faith through God's grace, two sacraments (called ordinances) of Baptism (adult only immersion) and the Lord's Supper, the independence of the local church, the church as a group of regenerated believers, complete separation of church and state, the immortality of the soul, and the ultimate triumph of God's kingdom. Because Baptists have had freedom of expression in the pulpit and pew, they are quite democratic. This means that liberal and conservative doctrines can be preached freely because each church is autonomous. Local churches license and ordain candidates for the Ministry. As a whole, there are few differences between Baptists today. The Southern Baptist Convention (SBC) tends to be more conservative or fundamental meaning they take a literal view of the Bible, while American Baptists tend to be more liberal in thinking. The problem is that every Baptist church is autonomous, that means no one outside the local church can control or tell it what to do. That means you can have very liberal Baptists and very fundamental Baptists in the same convention. That also means that any local church can come up with its own doctrine or beliefs and still remain Baptist.