Will a person attain the reward of being in the first row even if there is only one row in the mosque?

Firstly: 

The evidence indicates that the reward for praying in
congregation increases with the number of worshippers. We have explained
that in the answer to question no.
38194. 

The reward for the steps that you take to the mosque, no
matter how far away it is, is recorded for you with Allaah, as the Prophet
(peace and blessings of Allaah be upon him) said: “Every step that is
taken towards prayer is a charity.” Narrated by al-Bukhaari, 2989; Muslim,
1009. 

Muslim (665) narrated
that Jaabir ibn ‘Abd-Allaah (may Allaah be pleased with him) said: Some land
near the mosque became vacant, and Banu Salimah wanted to move there and be
close to the mosque. News of that reached the Messenger of Allaah
(peace and blessings of Allaah be upon him) and he said to them, “I have
heard that you want to move near the mosque.” They said, “Yes, O Messenger
of Allaah, we want to do that.” He said, “O Banu Salimah, stay where you
are, for your steps are recorded; stay where you are, for your steps are
recorded.” 

Al-Nawawi (may Allaah have mercy on him) said: What this
means is stay where you are, for your steps will be recorded and the many
steps that you take to the mosque will be recorded for you. Banu Salimah was
a well-known tribe of the Ansaar. End quote from Sharh Muslim,
5/169. 

It should be noted that the criteria for deciding whether to
pray in one mosque or another includes other matters besides the number of
worshippers and the number of steps taken to reach the mosque, such as
whether the imam and congregation adhere to the Sunnah, how keen they are to
establish prayer as enjoined by Allaah, with proper focus and humility,
straightening the rows and other things that make the prayer more complete
and perfect. In some mosques there may be circles for teaching or memorizing
the Book of Allaah, so a person should have a share of that and should not
miss out on such things, even if the number of the people in the mosque is
small. 

Proper understanding dictates that one should weigh up the
quality of one’s deeds and prioritize accordingly, and strive to attain
reward as much as possible. 

Secondly: 

There are several ahaadeeth about the virtue of the first
row, such as that narrated by al-Bukhaari (615) and Muslim (437) from Abu
Hurayrah (may Allaah be pleased with him), according to which the Messenger
of Allaah (peace and blessings of Allaah be upon him) said: “If the
people knew what (reward) there is in the call and the first row, and there
was no other way to settle the matter than drawing lots, they would draw
lots for it.”  

Abu Dawood (664) and al-Nasaa’i (811) narrated that al-Bara’
ibn ‘Aazib said: The Messenger of Allaah (peace and blessings of Allaah
be upon him) used to walk up and down the rows, wiping our shoulders and
chests, and he would say, “Do not let your rows be ragged lest this create
disharmony in your hearts”, and he used to say, “Allaah and the  angels send
blessings on the front rows.” Classed as saheeh by al-Albaani in Saheeh
al-Nasaa’i. 

This was also narrated by Ibn Maajah (997) with the wording:
“Allaah and the angels send blessings upon the first row.” 

What is meant by the first row is that which is directly
behind the imam, whether there is a barrier or not. And it was said that it
is the first complete row that is directly behind the imam, or it means
those who came to the prayer first, even if they pray in the back rows. 

Al-Nawawi (may Allaah
have mercy on him) said: The first view is the one that is sound. This was
stated by the scholars. The other two views are clearly mistaken. 

End quote from Fath al-Baari, 2/244. 

It makes no difference whether there is one row or several
rows in the mosque. The row that is closest to the imam is the first row,
and its people are promised reward as indicated by the general meaning of
the ahaadeeth. 

And Allaah knows best.